Fvck the single player, this game is a multiplayer game FOREMOST and single player/co-op SECONDLY. The single player mode only takes a few hours to beat for **** sake. So I will judge it accordingly...
Yes the multiplayer in MW2 fails (PC version) compared to WAW. There was a lot of nice new things added to multiplayer (more kill streaks, more attachments, more customisation, more balanced perks, etc) but when it comes down to gameplay it's just not as good. They nerfed strafe-spraying and hipfire accuracy from what I can tell, which was the ultimate counter to sh1t cvnts who just camp in 1 spot and aim in 1 spot all game. MW2 actually PROMOTES this type of crappy game play; sit in 1 spot and zoom in and kill the people that run into your crosshair. Yeah lots of skill involved in that, you can clearly tell the game developers have autism or are total sh1t cvnts themselves. If you try run in to kill people you usually get slapped because you don't even get time to zoom in because you are moving (unless the enemy is terrible) and if you don't zoom you can't hit anything, especially from medium range and long range.
There's more maps but they're big, there's more camping spots than WAW and it's hard to see people, which again promotes people sitting in 1 spot because you can't see them until it's too late.
Counter-Strike, World at War are brilliant games and MW2 could've probably been better than both but no they had to **** it up. This always happens with games nowadays (idiot game developers who don't know anything about balance, probably the most important aspect of competitive games like this) so I'm not holding my breath for a better FPS than CS 1.6.