Not as good as the original but still a great buy!
Graphics- The graphics haven't changed much since the original here but there are some noticeable improvements in them.
Gameplay- Just like the first fairly easy to learn.
Story- Not much of a story here. You basically know the story without even playing the game. There is a zombie apocalypse and you play as 1 of 4 survivors attempting to survive and escape. There really isn't any story what so ever. Well technically there is but you know what I mean.
Replayability- This all depends on whether you have Xbox Live or not. If you do you will be addicted to this and be playing for countless hours in front of the TV. If you don't however it might not last you quite as long in single player but it is still a very fun game to play and you will come back for more eventually.
Fun Factor- This is one of the most entertaining and fun games I've ever played. From times where a Boomer vomits on you and the Horde comes charging to attack you to extremely threatening Tank attacks to other times when a jockey jumps on the back of a comrade and everything in between. You will not get bored with this game guaranteed.
Overall- Overall L4D2 is a great game and a great buy. It improves over the original with the addition of melee weapons, and slightly better graphics but it is missing the original's atmosphere which is only redeemed in the Hard Rain campaign. Still a great game to pick up and put in your collection.