PSO I & II is on both xbox and GC, the xbox version CAN be played offline but you need an xbox live account to activate the game. However, PSO I & II PLUS is GC exclusive as far as I know. The GC version of I & II has slightly different graphics, xbox has downloads and voice chat. I would say that there are differentish games bu trather similar, although the PLUS version is exclusive.

Godzilla Melee on Xbox has downloadable features and i think one or two extra characters, if that matters.

Great list though!