just the gameplay alone for HL2 is better than halo 2.. I find counterstrikes weaponsets to be more fun simply because of how cheesy some of the players can make the halo 2 weapons look.. (such as jumping down a cliff while firing a sniper rifle.. a headshot would still be possible in those conditions with the halo 2 engine, when we know that would be unlikely with counterstrike (which I enjoy the unpredictability))
I love the intense feeling you get from CSource. I dont really care if its not as realistic as possible, but the gameplay is so refined that it feels just right when you shoot somebody, or when you move around. And especially with physics, and awesome graphics, its still a great game.
Havnt played Halo 2, but Halo for the PC multiplayer felt just like any other multiplayer Ive played, and considering its near competition of UT2004, its not fun at all. The weapons are completly unbalanced (fueld rod gun anybody?, or the lack of power the assult rifle has) and the maps are so-so.