DI is immersive, with some flaws that can kill that... like things respawning. It's also RPG-like, Fallout 3 style. You have attributes you can raise with experience points. It's not perfect, but it works okay. The game was nowhere near as good as the preview trailer looked. But it's very fun for the current price. Scary, immersive, lots of melee, smashing into those things with vehicles, etc... I really like it overall. I've put in many hours and only just reached ACT II. I'm hoping for different stuff at this point. Not sure if i'll ever finish it since I already have DI Riptide ready to be installed as soon as...
It's different than L4D2 but you can still have people online playing with you. That aspect I don't use, but it does seem like fun that way when I've tried it.
I only just started State of Decay and it's not bad. Easier than DI, but sort of kind of fun.
LFD2 is so hard without human players. I couldn't even get passed the rollercoaster level. It was like a Titanic level that was unbeatable, I'm going down and it was just "how sooon!"
Since you're into zombie games, the trailers for Dead Island 2 and Dying Light are up. Both look terrific. I saw some gameplay footage from Dying Light and I've added that to my steam wishlist. Looking forward to that one.