I will say what I think to be the problem for who dislike it:
-It tries too hard to be a portable SOTN.
-Colors, it was made very bright because at the time GBA SP didn't existed and people disliked that they cant see properly the game in CotM, so they choose to give a "aura" to some enemies and playable character and brighten all colors, but then when GBA SP and Nintendo DS came out, it was too bright and people complained about that.
-Playable characters sprites aren't well made if compared to all the rest of the game.
-Music quality is outdated, also if you mix it with the dissonance style of music then a lot of people wont appreciate it since they cant decipher or simply doesn't like it.
-Enemies and save rooms tries to be identical to SOTN counterparts, also portals do that too.
-Bestiary without description
-Juste is like Alucard and even leaves a after-shadow.
-When you get your first magic book, you hardly will use hearts after that.
-Lack of difficulty, sure you can die, but there is a plenty of ways to destroy enemies very fast, even more if you have money to spend on mana potions.
Things like that. Since I know all of those flaws (some aren't really flaws and are even nitpicking from people) and still likes this game to the point of it being one of my favorites if not THE favorite, I must really love it lol