I liked Days. Was it repetitive? To a certain degree. But I liked the dynamic team system and since I'm a completionist at heart I loved getting all the emblems and rewards from the missions.
Same thing, it was a bit repetitive but I actually enjoyed the game and I ended up collecting everything and getting all of the hidden characters like Sora. Too bad I had no one to play Multiplayer with, though T.T
Back to the topic. Someone mentioned that challenging is not fun but to me the more frustrated I get the more it drives me to change my tactic and beat a boss. To be challenging doesn't have to mean that the boss can kill you wit one hit (although the moments when Sephiroth drains your life and you have to heal yourself before he kills you made my heart race the first time). Challenging doesn't have to mean that the boss is uber stronger than you are but a boss that forces you to change tactic to more effectively deal with it. The Reaper with the coins forced the player to not resort to hack and slash all the time.
Exactly, I really dislike how most bosses now render your health useless as they always bring your health down to 1 with one hit no matter what. It was cool with Sephiroth, though, since he had an attack solely devoted for that.