I got The Conduit because it was an FPS for the Wii (which had already been done) promised nice graphics, which it didn't quite deliver on (not that it really matters), and good, customizable controls (possibly the main draw for me, and which it really delivered on well). I wasn't disappointed with it (I even played enough to get all the achievements), but there was lots of room for improvement.
Now that the sequel is (finally) coming out soon, I can't remember what it was that drew me to pre-ordering it in the first place. I wasn't attracted to the improved campaign and graphics, and the controls are about as good as they get. Yet I've already paid for it in full, and don't plan on canceling that.
If nothing else, I'll chalk it up to giving money to a development studio that I wish to support, so that it can continue to produce quality games and hopefully raise the bar for FPSes, and other genres in the future.
Life's no fun if you take it seriously. http://imgs.xkcd.com/comics/duty_calls.png
Supporting HVS, like you said, is one reason. That probably shouldn't be your main reason though. I'm thinking the splitscreen multiplayer, the (hopefully) much-improved online, the new guns and better-designed maps. Those are some of my main ones, anyway...