I also thought HL2 was a bit disappointing. I also thought the game was a bit short. But take this into account:
1) I don't do online, multi-player gaming, so I'm ONLY talking about the single-player game.
2) The single player game was good, but not great like HL1. I often felt HL2 was really only a vehicle for getting me to play multi-player, and a lot of complexity, puzzles, outright fun was dropped in favor of developing a more robust OL section, which is fine.
So if you're gonna deathmatch with your friends, It'll be fine. But I was disappointed with HL2 singleplayer.