I liked that, in Digimon World 1, getting to level Ultimate was a very hard thing to do, and there were no Megas, Ultimate was all you could get, so when you faced Machinedramon it was all more special, when you saw the final boss was a mega level digimon, the only one in the game, and you knew this was it, the final fight... I don't know...
I would like a game like that, with more rookies and champions and stuff, but less Megas and less fusions, not because I don't like them, but because that makes the final battle way more intense.