The game is just as good as the hype said it would be.
From the first campaign will play, you instantly notice changes from the predecessor. The campaigns start off just like the ones in Left 4 Dead 1, but you soon discover melee weapons, boomer vile in a convenient glass jar, higher caliber pistols, e.t.c. Most gamers believe that it is the melee weapons that really set the difference between this game and its predecessor. Your weapon options range from cricket bats, guitars, axes, baseball bats, and even an occasional chainsaw. Melee is probably the biggest new addition to the game, but it certainly is not the only one. In Left 4 Dead 1, you would start off with basic low quality weapons, then about mid second round you would discover high quality, military grade weapons. The same is not true for Left 4 Dead 1, as there is also a mid grade. The basic weapons are pistols, oddly made machine guns with a homemade silencer, and maybe a baseball bat. Later, however, you may discover a high grade Spaz shotgun, but only an extra pistol. Valve done a very good job of mixing up the weapons and diversifying the game this time around.
Valve also noticed some of the strategies that players used in Left 4 Dead 1, and decided to come up with ways for the apocalyptic zombie special infected to crush those strategies. You have your original special infected from Left 4 Dead one playing in this sequel, as in the Hunter, Witch, Tank, Smoker, and Boomer, however, you also have three new special infected, known as the Charger, Spitter, and Jockey. The charger is a large special infected with one giant, strong arm, and one very weak, useless arm. The Charger is called by it's name because of its speed. The Charger will run at a survivor, grab them, run away with them "only in a straight line" and then smash them against a wall or on the ground. This was made to ensure that the person(s) "yes, the charger can grab more than one survivor at a time" and separate them from the group. The Spitter, which simply spits noxious acid at you, does just that and forces you to move from the area you are in, which is especially frustrating if you are trying to stick to a corner while making your last stand, awaiting rescue. The final new special infected is called the Jockey. The Jockey itself does little damage, but can lead you into death very quickly. The Jockey jumps on your back and forces you to walk in a particular direction, which can lead you to Spitter acid or right into the Tank.
One thing that does kind of set a drawback though is the AI. It is still fairly stupid, as it will sometimes walk directly into your line of fire. Of course, the AI can't through pipe bombs, though there is some improvement. Other than that, I see no problems with this game, and I think it has and will continue to be the best zombie shooter for some time to come.