DKII on 06 October 2008
Never once used the GBA slot so that's not a concern for me, but the reduced battery life definitely is.
Were you this upset when the DS was revealed to be unable to play GB/GBC games? sheesh, it happens. DSi is basically a new handheld that is backwards compatible with DS games, but just as the DS didn't go two generations back, neither will the DSi.
