Seeing as the only person commenting is answering just to get points, I'll actually try to help you out.
(EDIT: seems someone else commented while I was writing this monstrosity, and they were helpful :) )
I've played a few good zombie games, and each has their pluses. But, it is very hard to rank them due to these differences...
I have not played any of the L4D's (yes, I know, a tragedy D:), so I can't rate them. I am only rating games I have played (duh), and I'm rating them all. So, if it isn't on the list, I haven't played it.
1) Dead Rising 2: Off the Record
- Due to the "Free Roam" mode, this is my absolute favorite of the Dead Rising series. And since Dead Rising has to be one of my favorite zombie series (or game series, in general) because of its extreme versatility and creativity in weaponry, it is undoubtedly my favorite zombie game.
2) Dead Rising: Case West
- Even though this isn't an official installment in this series, this game has the second person following you around. This introduces a unique gameplay capability that happens briefly in the other games of the series.
3) State of Decay
- Just a foreword: I have only played the demo so far. I like this game. It has a central base, which can be fortified (like CoD: Zombies), but it has the free roam capabilities, like Dead Rising. It lacks a unique inventory/weapons system, however. It also has somewhat abnormal controls, and the actually controlling feels clunky. The graphics are good, though I often get confused as there is very sub-par turning that makes it look like you're sliding on ice.
4) Dead Rising 2
- Love the story, and love all the classic Dead Rising customization features. Haven't tried the multiplayer yet. FYI, this game is FREE WITH GOLD until the end of the month, so might as well download it.
5) Dead Rising: Case Zero
- The only reason I rate this down is due to the short story and limited customization. But, it's only $5, and is otherwise like every other Dead Rising.
6) Call of Duty: Zombies (In general)
- I've only played one version of this series (excluding the iOS versions), and I rather liked it. It was either WaW or whatever (wasn't mine, it was my cousin's, and I only ever played it once). While I liked it, I felt very restricted with it, being limited to the mystery box or the wall guns, and limited to a small enclosure. However, I liked the wide range of guns you could wield.
7) Dead Rising
- I can honestly say I have no clue how this series survived if this was the first. This has the weirdest controls I have ever used (and I played A Tale of Two Brothers). Other than the controls, the storyline is fine. Graphics fine. I just HATED those stupid controls!
I assume by "zombie games" you don't mean games like PvZ, so I've only included the FPS/TPS that I could remember.
Hope this is a thorough response, unlike the Sony fanboy who said Last of Us just to get the answer points ;)
LOTS of gameplay :)