It's hard to say. Youkai Watch is far more "Japanese" than Pokemon. Most of the Youkai Watch monsters are directly lifted from Japanese folklore. That might not mean much, though, as kids in the west might just assume they're just really weird designs.
The Youkai Watch anime isn't quite as battle-centric as the Pokemon anime, either. It's more about the kid solving problems with and for spirits and youkai, plus a good deal of comedy.
I don't think it will be a massive success but, as with anything, it's going to depend on how much money they're willing to pour into marketing.
Yeah, yeah, that's what I was getting at. That cultural barrier is very high for this game. Kids in Japan understand it, but it's like American kids will be confused as hell and it'll go right over their heads. To be honest, I don't even think Marketing can make this game a success in US. Like I said, I'll give it a go just to see what it's like but...you know.