only the us port is unplayable. i guess cave used a different graphics engine than the jp port, which eliminated slowdown. this is a huge problem though, as the scoring techniques players have been practicing for years won't work on the us 360 version. likewise, the us and jp versions have different leaderboards.
the port of guwange is pretty okay though. the 4:3 support is a little wonky now that they've patched it in (it actually zooms in on the natively rendered 16:9, which means the menus are zoomed in on as well), but once you set it up it works fine.