I don't think it's a complete fail, but there are a lot of failing aspects.
One of the biggest complaints I've seen is spawn points. They sometimes are so unfair to either the spawner or the killer, it's ridiculous.
All-in-all, I think IW did a great job layering that customization part that if you actually went through the game hack free, putting the time in to get everything would take you a while. Which for me, I like. Gives me lots of things to do, figure out how things work better for what situations, etc etc.
Though for everything IW did to improve over the first modern warfare, they left a lot of things unpolished and could have put better quality into it.
And not that I really have anything against hackers and what they want to do to their game, but this game apparently was too easy to crack.