Guild Wars is definitely gaining momentum in America. It ranks pretty far up in the sales charts and G4 is constantly talking about it. I never cared for MMORPGs, so I wouldn't know either way, though.
As for "underground" games that I like, what else can I say besides...
JET SET RADIO! adio... adio...
adio...
Back in the Dreamcast days, I was in love with that game. It got to a point where I could literally come home every day after school and beat it in a matter of hours. And I did. Every day.
Loved it.