Other than the reasons you brought up, tb86, I understand a lot of people didn't like 02's ending because it was too happy (well, except for Oikawa dying, of course), whereas Adventure's ending was too sad. Sort of a neat balance, if you will.
Still, I personally think it stands as one of the all-time lamest endings of anything I've ever seen, all the more apparent since I realized Digimon was a pretty stupid show to begin with. (I mean, as a kid, I loved the hell out of it, even though I knew how insanely overwrought it was, but nowadays I don't even bother revisiting it because I've moved on to better, more mature anime. I just hope to God I don't feel the same way about Fairy Tail, especially considering how incoherent I think the current arc is. Okay, end digression.) Personally, I like to think of it as a lamer, more goody-goody anime version of how Roseanne ended. 