Definitely a 9:
Pros -Very attractive environment and landscapes
-High level of graphical detail for such a large game
-Expansive landscape that never feels stale or tedious to explore (save going back to the police station 9,781,451 times)
-Very multiplayer-friendly but by no means multiplayer-reliant
-Casual game experience that makes for great gameplay when playing with friends
-Gruesome and gloomy atmosphere gives a lot to the survival feel of the game
Cons -Riddled with bugs and clipping issues
-Lack of enemy diversity can make fighting zombies feel repetitive
-Lack of sufficient ammo makes me reluctant to use firearms
-Lack of manually adjustable difficulty may make gameplay boring to some seeking more of a challenge
Additional Notes I find replayability can be had by doing funny crap (attempting a playthrough using nothing but fists save areas that make using fists exceptionally impractical). This is possible due to the casual nature of the game in which dying doesn't pit you against any markedly detrimental penalties and enemies retain damage they received prior to death. Especially fun with friends.
Shock damage is OP. Defeated endboss at level 45 in 4 shots. Stocked up ammo, weapons, and medkits expecting an epic battle that required tons of strategy to defeat (possibly multi-stage). Popped him with 2 rounds from a pride heavy pistol with the second one scoring a crit. Ran up, kicked him to keep him down, stomped him, and then sat there thinking "...Did I just beat the game?"
The lack of in-game tutorials, though it helps to speed up play, doesn't really allow one to thoroughly understand the game. I'm never told that by breaking 2 limbs on a walker they instantly die. I'm never told jump kicks do more damage and instantly knock down any walker/infected upon contact. I'm never told what effects mods have until after I've applied one to a weapon. Not saying that a tutorial should be included for ever little thing, but an in-game encyclopedia wouldn't hurt IMO.
Overall I give it a 9 simply because it's really damn fun to play with friends which is something I've not seen the common game succeed in since the Nintendo Gamecube. Despite its lack of difficulty adjustment and game imbalances, it's one of the better games I've played in recent times easily clocking in over 20 hours within 3 days of purchase.