I'm stuck between Halo Wars and Reach.
Most people who played Wars were probably FPS folks who strayed over to it because it had "Halo" in the title, and some of them probably haven't played enough RTS to realize how terrible Halo Wars really was in comparison to other representatives of the genre. Halo Wars to an experienced RTS player is baby's first strategy game; it has no depth of play and no need for any real "strategy" at all. It's one dimensional.
It's bad, but then again, Reach is...well, it's Reach. I wish they had at least stuck to the story they laid down in previous games and books; then it would have at least had an interesting campaign. But they couldn't even manage continuity within their own damn series. How sad is that? I at least like SOME aspects of the multiplayer, although it's definitely a downgrade from Halo 3, but I'll just go ahead and say that Reach's campaign was awful and leave it at that.