Starcraft 2's multiplayer is quite amazing (far better than any Halo title I've played, and I've played them all) as long as you stay the hell away from Ranked/League matches.
The single player campaign is surprisingly well done, with the missions being fun, varied (not easy to do in an RTS), and well-balanced for a variety of skill levels.
Halo Reach...well, some of the fan-advertising I've seen for it is already claiming the title of "Game of the Year" before it has even been released, and I question games built entirely on hype (I hate self-pretentious games that "claim the throne before they're crowned King", so to speak).
If you want Halo's multiplayer...well, I'm waiting before passing judgment. I speculate that it will be more of the same, but at least this time we won't have to worry about as many griefing racist 13 year-olds clogging the VOIP channels.