Lost Magic/YMMV

Crowning Moment of Awesome: A rare, player-initiated example. The "[Element] Dance" spells have Isaac running up to the target monster/enemy and smacking the everloving crap out of it with his charged wand..
Game Breaker: In the form of a Last-Disc Magic, the aforementioned Elemental Dance Spells. Whilst their range is sub-par, you're invincible whilst you use them, and you slap the selected the selected enemy until it dies.
Goddamned Bats: A small part of Lost Magic is going straight to hell for forcing us to pay attention to - next to an overly long list of other things - infinitely respawning enemies coming from spawn circles that can only be blocked by putting one unit of yours on it, permanently. Some maps have up to five of these, forcing you to leave much of your army as guards. And sometimes, enemy units sneak up to them and kill them whilst you're away, or you accidentally use the one spell that teleports all units close to you from across the map, etc. etc. In short: Infinite respawn = Nintendo Hard.
Surprise Difficulty: Ohh, the colours are so bright and the lead looks 10. This has to be an easy kids game... right? OH **** !
That One Boss: The Final Boss certainly counts, even more so when she Turns Red. However, depending on your monsters, items and which of the 400+ spells you bother to remember, all of the bosses can be anywhere between DS-tossing Nintendo Hard and Curb Stomp Battle.To put this fight into perspective, the reason most bosses were a challenge in the game was that they camped around healing crystals casting spells, and sending legions of enemies toward you. Most of the challenge consisted of covering up monster portals, killing or trapping said monsters, and getting the boss away from the mana crystal within a time limit. The Diva of Twilight's first form is harder than any of the bosses in the game, in her first form. Even if you had to face all the bosses in one location consisting of a composite map of all terrain and monsters in their respective areas, the Diva would still be much harder, in her FIRST FUCKING FORM!!!!! There is no harmful terrain, no harmful monsters, no mana crystal,... and the Diva is still stronger than any other boss in her FIRST........FUCKING............................................FOOOOOOOOOORM!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! The hardness of the Diva comes from only 6 out of the 400+ spells in the game. The spells in order of least to most annoying are; close proximity mines that she puts right in front of your path, faster than you can run away; unblockable conversion spell that converts everyone in your party into living bombs;a cloud that turns your monsters against everything and lasts for half a minute;a spell that instantly turns all of her stats up to eleven;a long range teleportation spell with unlimited range; a full healing spell that will be activated automatically within 10 seconds upon receiving information about low health. the last two spells might not seem that annoying because of the simplicity of the former and the slowness of the latter, but the most inadequate stats of your characters are your range and speed (meaning she can outrun you with teleport and heal while you're catching up to hit her with a spell.This is all timed. If by some stroke of luck , or your divine ability to cheat at video games, you make it to her second form, she will not only use all the same tricks above, but she will also summon the most powerful monsters in the game from portals, and camp out at various points for the duration of the fights surrounded by her pets. There are also 5 monster portals in contrast to the previous bosses which had 3. The cloud of evil gas that she spams doesn't affect her monsters. This raises the interesting question to where the player's god is.