Except for the Zero series, every other Mega Man game released for DS was an RPG, which doesn't hold the same interest for me. Never played a Front Mission game. Fire Emblem is, again, an RPG I don't have the patience for. Never played Advance Wars.
I'm sure there are lots of games that are actually good for the system that I would enjoy, I just couldn't find them when I had one and couldn't be arsed to keep up with it for the couple of games that would have been worth picking up. Now that I have a 3DS I've been trying to keep up with the games a bit more, since there are some out there that I really want to play, but the DS just didn't not hold any interest for me.