Why to people always focus on Alpha 16? That was probably one of the absolute buggiest versions that existed. Drive down a road and your minibike would teleport into a hill next to you with you on it. Managing servers was almost a complete nightmare unless you used several API mods to counter a number of the games issues in the world.
It was probably the first version that started taking away most of the survival aspects. Oh wait.. THAT"S why you like it so much. Alpha 16 was basically easy mode with no challenge and infinite food and ammo.
Personally, playing single player only, I never found it particularly buggy.
Anyway, my preference for A16 is simply that horde nights (and consequently base building) were much more fun because they weren't easily exploitable. I've said this before (and I'll most likely say it again) but in A16 I loved coming up with base designs, building them, and seeing if they worked. Since A17, I've had a base not work as intended a total of once, because I was unaware they'd changed the length of the path AI would follow, and thus built my base too large.
Horde night has become entirely predictable, and therefore boring. There's no more trying to find ways to control the zombie's movement, instead you just control it easily. Now I dream up horde base ideas, and then never bother to build them because I already know if they'll work or not. That wasn't the case in A16.
Also, my favorite mod of all time (Valmar's Overhaul, I really loved how improving your skills was what unlocked more recipes) was for A16, so...I'm a bit biased there.
That said, there are changes since A16 that I like, so if I could just have unpredictable zombie AI again, I'd be fairly happy, I imagine.
As an aside: As someone who actually doesn't like survival games particularly, I'd have probably put less than a hundred hours into 7 Days if it was a hardcore survival experience, instead of the thousands I have put in. I don't mind that kind of thing once in a while, but it's not something I want to play regularly. I largely bought the game because I was looking for Minecraft with more challenge, and there weren't really any Minecraft mods at the time that made any sort of base defense necessary.