I've had this camera for about a month now and I really enjoy using it, more than my D600. The reason I have this Sony now is because one of my Nikon D600's was stolen from my car a month ago. It was pretty terrible, but shit happens. Then the time to purchase a new camera came. The options I had in mind were the Sony A7, another Nikon D600, a Nikon D800, or a Nikon Df. I ended up going with the A7 and Sony FE 55 because I got it for $1000 off retail brand new. It was too good to pass up.
- Weight/Size: Sooo much smaller and lighter than my D600, obviously. I just didn't realize how much of a difference it was in real-world situations. I can sling the A7 around my neck and hardly even feel it as I walk around the city. The D600 wasn't terrible, but the A7's weight puts it to shame.
OLED Viewfinder: This is the feature I was the most excited for. Since I'm pretty blind and refuse to wear contacts/glasses, the viewfinder being an actual screen helps me out a ton over a traditional optical viewfinder! Being able to see what you're going to end up with is amazing. Plus focus peaking/magnification are two features I can't live without now. Every time I go back to my D600 at the studio I have a hard time readjusting to the optical finder.
Image Quality: Amazing. Sharp. Crisp. The photos that come out of this camera are truly amazing. I really don't miss using the D600 one bit. The colors pop without being too over-saturated and the in-camera lens corrections make barrel distortion and chromatic aberration pretty much nonexistent. If anything, the only downfall I see in the image quality is that you start seeing grain at about ISO 800. Maybe the A7s will perform better in low-light situations, not that the A7 is bad. I'll include samples at the end.
- AF: I'm not too fond of the autofocus system in the A7. It's a hybrid system with contrast AND phase detection, while the A7r only has contrast detection. I was so used to picking my focus points on the D600 and being able to count on the camera to focus correctly the first time. On the A7 you can pick a "zone" if you want a specific area focused, but you can't select preset points like on regular DSLR's. It usually means I'll miss 1-2 shots out of 10, and while it's not much it can still cause you to miss "the moment". Hopefully they improve with the next generation.
- Battery Life: It's pretty simple I guess, small body = small battery. The A7 actually uses the same battery as the rest of the NEX family so if you a few already that's a plus. It lasts about 400 shots, so I'm constantly turning the camera on and off as I'm shooting. And the vertical grip is about $300 from Sony. I'd rather keep spares in my pocket and swap them when needed.
- Lens Line-Up: Since the A7/r are full-frame, Sony had to release some lenses to go along with the new system. There's only 4-5 out right now I think; 24-70 f/3.5-5.6, 24-70 f/4, 35 f/2.8, 55 f/1.8, and a zoom I think. The only ones that caught my attention were the 55 f/1.8 that I own and the 35 f/2.8. I almost bought the 35 but I'm waiting to see if they release a 35 f/1.8 or 2. I'm still unsure about the FE system but who knows what can happen within a year.
I personally think the Sony A7 is the best mirror-less camera system out right now and if you're hesitant about getting one, don't be and go for it. You will not regret it. If you're able to, I'd say wait for the next generation so they work out the autofocus/battery/lenses. If you're in need of a camera now and don't do too much work involving motion, I'd say the A7 is a no brainer.