I think the campaign in halo is great.... just that I think halo is more played for its online aspect. and I belive that half life is not as good in a sence as I just never got a huge feel for it.

 

the campaign is a great part of the game. but the multi-player is what has made it famous

 

i have always liked, not only the story lines in half-life better...but in my opinion the multiplayer is far, far better....because of the fact that you can heavily mod the source and HL1 engines and make games that are great, and usually have A+++ multiplayer...