This game is not without its flaws. But I still thoroughly enjoyed it from start to finish. It's funny that that the limited GotY edition has just been released and I've literally just completed the game. I played the first half when it came out and I've only just gone back to it and completed it all.
The game essentially starts off on an amazing looking beach resort and you, as the main character, discover what has happened to the island of Banoi: there's an infection and zombies are roaming the streets. The game takes you from the beach resort in Act 1, to a city in Act 2, a jungle in Act 3 and finally a maximum security prison in Act 4. It took me over 26 hours of game time to get to the end (albeit I tried to complete the majority of the challenges available, secondary as well as the main ones).
Combat is a double-edge sword (excuse the pun). Sometimes it is thoroughly satisfying and gory, other times it's very frustrating. The graphics aren't amazing, but the settings are incredible, particularly the opening beach resort; it's surreal to be fighting zombies around swimming pools, but it doesn't feel cartoony like Dead Rising, it actually feels real and right, like this could actually happen.
I loved the range of challenges to do, and enjoyed the overall flowing storyline, but it could be a bit weak and clumsy in places. But those flaws didn't put the game off for me at all. I kept bashing away with it, struggling in certain areas and getting annoyed at the damn Infected zombies (as they are very quick and constantly hound you).
But nevertheless, amongst its weaknesses there is a great game to be found. I found it very enjoyable in most places and found completing challenges very satisfying. Overall this is one of my favourite Xbox 360 games (and I've owned/played a lot). Now that I have just completed it, I also plan to go back to finish off more achievements and play through some of the campaign with the other three main characters too.
As a final note, the co-op actually works very nicely, and is quite unique compared to other games. You can dip in and out of the co-op as you go, bumping into people, joining their games or allowing them to you yours. Ultimately the game is easier when you are teamed up with others as collectively taking down zombies is much easier. But it's nice to have the option of either working with others or going it alone whenever you want.
Overall, this is definitely not a perfect game, but it is still great, and definitely the best zombie game I've played to date. I'm reading the novel now too. :)