Left 4 Dead is excellent and i love it, ive got Gears 2 also which is an excellent game too. Far Cry 2 is also good but i find the long distances to travel and space between saves quite annoying. Over all the guy who says Left 4 Dead is rubbish must not play any multiplayer games as its one of the best to ever grace a console.
If he got the game expecting a long detailed story then yeah he will have been disappointed. However if he actually got the game knowing ANYTHING about it it wouldnt have been disappointed. As its essentially a multiplayer game thats best when played with others as there isnt really any story as such. Just 4 survivors going safe room to safe room. If you watch any videos or reviews you will understand what the game entails and its a blast. A game best played with friends who can work together and not be a lone gun as they die very fast.
Simply put Left 4 Dead is amazing if you enjoy 4 player co-op zombie shooters (in which there arent many). Valve just dont make bad games...