I love the game, too. When I talk about other things that could've been included, I don't really think of it as a diss. More of a "I wish this was here so I could play it, too." If they could've included the Symphony of Sorcery music somehow, or "Let's Sing and Dance" and "Isn't It Lovely" from KH2 Atlantica, and all the opening / closing themes, orchestra music, etc., it would've been glorious and addictive to play all those. The ability to change outfits for Riku and Sora would've been nice, but it's no big deal to me.
I actually don't even care about bosses, although I understand why others do. A lot of people like combat more than anything else, I guess. I did think the other day how fun it would be if there'd been a boss of Dragon Maleficent prior to Ansem SOD. And how they could've had boss tracks that were done a little differently in some cases than the fights against one villain, like if you fought multiple of the lesser villains combined together. To give an example of what I mean by that, you know how in the bosses you would fight once, then defend, fight again, defend again, then fight one last time? For KH1, you could have a boss track with "The Deep End" near the end of those worlds where you fight Genie Jafar, defend, then Giant Ursula appears and you fight her, defend, then finally you fight Hades and defend. That would include some of the players of each villain group without putting everyone in there. For CoM, you could have one that combines Axel, Vexen, and Larxene (and then a solo battle against Marluxia). For KH2, you'd fight Xaldin, Saix, and Xigbar, for example, before the Xemnas solo battle. Or perhaps change villains when you're defending, too, so you could fit more in there (fight Xaldin, defend from Luxord, fight Saix, defend from Demyx, fight Xigbar last)? It would've been a really fun way to get all the notable faces in there.
I hope maybe in the future there will be a sequel perhaps that includes some of what wasn't there along with new music from KH3 and the games after it.