I bought a Sony A7 and a couple of lenses about two months ago to replace the Canon 5D Mk II that I had before. Here are my experiences with the A7 after two months of shooting. I've taken around 1500 shots on the A7, so these are still beginner stage thoughts.
If you're not familiar with it, the Sony A7 is a full-frame mirrorless camera at a reasonable (for full-frame) price point. It's small, it's light, and it's full-frame. The image quality is amazing. You can also find Sony E-mount adapters to fit pretty much any lens out there. If you have a cupboard full of vintage glass or want to fiddle with old Leica lenses or suchlike, the A7 lets you shoot those at full-frame with all the digital goodness of a modern camera. You probably end up adjusting the aperture and focus manually on adapted lenses though. There are AF-capable adapters for Sony A and Canon EF lenses, but the rest are manual focus only.
It's not too much of a problem though, since manual focusing on the A7 is nice. You can easily zoom in the viewfinder to find the right focus point and the focus peaking feature makes zone focusing workable. It's not perfect ergonomically, as your MF workflow tends to go "press zoom button twice to zoom in, focus, press again for even closer zoom, focus if need be, press zoom button again to zoom out, frame." What I'd like to have is "press zoom button, focus, press zoom button, frame." Or zoom in just one area of the viewfinder, leave frame border zoomed out so that you can frame the picture while zoomed in.
Autofocus is fiddly. Taking portraits with a shallow depth-of-field, the one-point focus mode consistently focuses on the high-contrast outline of the face, which tends to leave the near eye blurry. Switching to the small movable focus point, you can nail focus on the near eye but now the AF starts hunting more. And I couldn't find a setting to disable hunting when the camera can't find a focus point (like on Canon DSLRs), so AF workflow is a bit slower than I'd like. Moving the focus point around is also kinda slow: you press a button to put the camera into focus selection mode, then slowly d-pad the focus point to where you want it.
The camera has a pre-focus feature that autofocuses the lens when you point the camera at something. I guess the idea is to have slightly faster shooting experience. I turned the pre-focus off to save battery.
The camera's sleep mode is defective. Waking up from sleep takes several seconds. Turning the camera off and on again seems to get me into ready-to-shoot state faster than waking the camera by pressing the shutter button. Because of that and the short battery life, I turn the camera off when carrying it around.
The Sony A7 has a built-in electronic viewfinder. The EVF is nice & sharp (it's a tiny 1920x1200 OLED display!) When you lift the camera to your eye, it switches over to the EVF. Or if you get your body close to the EVF. Or if you place the camera close to a wall. This can be a bit annoying, but you can make the camera use only the rear screen or the viewfinder. Note that the viewfinder uses a bit more battery than the rear screen. Probably not enough to show up in your shot count though.
If you have image preview on, it appears on the EVF after you take a shot. This can be very disorienting and slows you down, so I recommend turning image preview off.
The rear screen can be tilted up and down. That is a huge plus, especially with wide-angle lenses. You can put the camera to the ground or lift it above your head and still see what you're shooting. You can also use the tiltable screen to shoot medium-format style with a waist-level viewfinder. The rear screen has great color and resolution as well, it's just lovely to use.
The glass on the rear screen seems to be rather fragile. After two months of use, I've got two hairline scratches on mine. Buy a screen protector and install it in a dust-free place. Otherwise you'll have to buy an another one, ha! The camera is not weather-sealed either, be careful with it. Other than the rear screen glass and the battery cover, the build quality of the body is good. It feels very solid.
The A7 has some weird flaring, probably due to the sensor design. Bright lights create green and purple flare outwards from the center of the frame. This might improve center sharpness for backlit shots, but for night time shots with a streetlight in the corner of the frame it's rather ugly.
One nice feature of the A7 is the ability to turn on APS-C size capture. This lets you use crop-factor lenses on the A7. And it also lets you use your full-frame lenses as crop-factor lenses. For instance, I can use my 55mm f/1.8 as a 83mm f/2.5 (in terms of DoF, in T-stops it's still T/1.8, i.e. has the same amount of light hitting each photosite). I lose a stop of shallow DoF and a bunch of megapixels but get a portrait lens that uses the sharpest portion of the frame.
Speaking of lenses, my lineup consists of the kit lens (a 28-70mm f/3.5-5.6), the Zeiss FE 55mm f/1.8 and an M-mount 21mm f/1.8 Voigtländer, mounted using the Voigtländer VM-E close focusing adapter. If I use the primes with the APS-C trick, I can shoot at 21mm f/1.8, 32mm f/2.5, 55mm f/1.8 and 83mm f/2.5. Wide-angle to portrait on two lenses!
The Zeiss FE 55mm f/1.8 is an expensive, well-built lens that looks cool and makes some super sharp images. Sharp enough that for soft portraits I have to dial clarity to -10 in Lightroom. Otherwise the texture of the skin comes out too strong and people go "Oh no! I look like a tree!" Which may not be what you want. If you shoot it at f/5.6 or so, the sharpness adds a good deal of interest in the image. It's a sort of hyperreal lens with the extreme sharpness and microcontrast.
The Voigtländer Ultron 21mm f/1.8 is an expensive, well-built lens that looks cool and makes sharp and interesting images, thanks to the 21mm focal length. Think portraits with environment, making people look like giants or dramatic architectural shots. It's manual focus and manual aperture though, so you'll get a lot of exercise in zone focusing and estimating exposure. The Ultron is a Leica M-mount lens, so you need an adapter to mount it onto the A7. One minus on the lens and the adapter is that they're heavy. Size-wise the combo is very compact, but weighs the same as a DSLR lens at 530g.
For a wide-angle lens, the Ultron's main weakness is its 50 cm close focus distance. But on the A7, you can use the VM-E close focus adapter and bring that down to 20 cm or so. Which nets you very nice bokeh close-ups. But blurs out infinity, even when stopped down to f/22.
The Voigtländer on the A7 has some minor purple cast on skies at the edges of the frame. It can be fixed in Lightroom by tweaking purple and magenta hues to -100. The lens has a good deal of vignetting, which is fixable with +50 lens vignetting in Lightroom. When fixing vignetting at high ISOs, take care not to blow the corner shadows into the land of way too much noise.
The kit lens is quite dark at f/5.6 on the long end, and it isn't as sharp as the two primes, but it's quite light and compact. And, it has image stabilization, so you can get decently sharp pictures even at slow shutter speeds. Coupled with the good high-ISO performance of the A7 and the auto-focus light, the kit lens is usable even in dark conditions. I haven't used it much though, I like shooting the two primes more.
Battery life is around 400 shots per charge. Not good, but I manage a day of casual snapping. The battery door seems to be a bit loose, I've had it open a couple of times when I took the camera out of the bag.
The camera has a built-in WiFi that the PlayMemories software uses for transferring images to your computer or smartphone. You can even also tethered shooting over WiFi but I haven't tried that. Transferring RAW photos from the camera to a laptop over WiFi is very convenient but quite slow. Transferring JPEGs to a smartphone is fast, though you want to batch the transfers as setting up and tearing down the WiFi connection takes about 20 seconds. When you're shooting, you probably want to switch the camera to airplane mode and save batteries.
I ended up shooting in RAW. I couldn't make the JPEGs look like I wanted out of the camera, so hey, make Lightroom presets to screw with the colors. The RAWs are nice! Lots of room for adjustment, good shadow detail, compressed size is 25 megs. You have to be careful about clipping whites (zebras help there), as very bright whites seem to start losing color before they start losing value. The RAW compression supposedly screws with high-contrast edges, but I haven't noticed the effect.
Due to shooting primarily in RAW, I find that I'm using the A7 differently from my previous cameras. I used the Canon 5D Mk II and my compact Olympus ZX-1 as self-contained picture making machines. I shot JPEGs and did only minor tweaks in post, partially because 8-bit JPEGs don't allow for all that much tweaking. The A7 acts more as the image capturing component in a picture creation workflow. Often the RAWs look severely underexposed and require a whole lot of pushing and toning before the final image starts taking shape. The colors, contrast, noise reduction and sharpening all go through a similar process to arrive at something more like what I want to see. I quite like this new way of working, it requires more of me and further disassociates the images from reality.
The camera has 16:9 cropped capture mode, which is nice for composing video frames. The 16:9 aspect also lends the photos a more movie-like look. The resulting RAW files retain the cropped part of the 3:2 frame, so you can de-crop the 16:9 photos in Lightroom. Note that this doesn't apply to the APS-crop frames, the APS-size photos don't retain the cropped image data.
I found that I can shoot usably clear (read: noise doesn't completely destroy skin tones) photos at ISO 4000, which is really nice. ISO 8000 and up start losing color range, getting magenta cast in shadows and light leaks when shooting in dark conditions. Still usable for non-color-critical work and very usable in B/W.
Overall, I don't really know why I got this camera and the lenses. I shoot too few images and video to justify the expense. The quality is amazing, yes. And it's not as expensive as a Canon 5D Mk III or a Nikon D800 either. But it's still expensive, especially with the Zeiss FE lenses. I feel that it's a luxury for my use.
The Sony A7 is too large and heavy for a walk-around camera strapped across your back and too non-tool-like for a total pro camera. I was trying to replace my old Canon 5D Mk II with its 50 f/1.4 and 17-35L f/2.8 with something lighter. But this is not it. The A7 has great image quality but the workflow is slower. And while it's light enough to throw in the backpack and go, it's still large and heavy enough to make me not want to dig it out. For me it sits in the uncomfortable middle area. Not quite travel, not quite pro. For occasional shooting it's great! Especially if you get a small camera bag.