So I was playing this for a few hours last night.
It's largely exactly the same as the mod in my opinion. There are some improvements that justify the purchase for me though.
- The crashing is a lot better as I haven't crashed once yet after a good 4-5 hours of play.
- Connection issues are mostly gone, didn't see any lag and didn't get any disconnects or have trouble connecting to servers as I often did in the mod.
- More buildings can be entered than in the mod and there seems to be more loot to be found, with more variety.
- More items in the game with more options how to use them such as tearing a shirt in to rags to be used as bandages.
At present there doesn't seem to be many zombies at all in the game, I only saw 4 but wasn't really exploring towns much. It's still impossible to find your friends, I couldn't find 3 of mine the entire time we were playing, I did find other players though.
I wouldn't recommend people to buy it if they already have the mod, but I don't regret buying it as I much prefer to have it on steam and not suffer the connection issues. I was expecting more really, but we'll see how this goes.