These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
YMMV: Rogue Legacy
Anti-Climax Boss: Alexander, the Forest Guardian. After the Castle Guardian subjected you to Bullet Hell the likes of which you hadn't seen, you're likely to be all hyped up for an epic confrontation... only to find that he attacks in a very simple and easily-dodged pattern. He does spawn mooks, but that makes him easier, not harder, since it means that you can use Vampire and Siphon gear to refill your HP and MP.
The Guardian of the Land of Darkness, Herodotus, could also qualify. The boss of The Maya, Ponce de Leon, takes a lot of coordination and luck to defeat, especially if you aren't playing as a magic-based class, as he lays fire traps down everywhere and constantly rams you for massive damage. Herotodus, on the other hand, is a giantAsteroids Monster, thus the HP/MP refilling strategy works especially well in his case. The pieces transform into Gravisors when defeated in their smallest form, but those are relatively easy to dodge considering you're already running around dodging the split slimes. Considering he's the boss of the most challenging area of the game, it's quite a letdown.
A patch makes things slightly better, as the blobs now have a dash move in addition to leaping.
If you're good at kiting, even Ponce de Leon can be this as well as he can't do much besides constantly chase you. A single retribution rune can help destroy the wandering spike balls, and if you want an even easier time the Barbarian King/Queen can shout to destroy the trailing fire.
Alternative Character Interpretation: Johannes is labeled as a traitor and has his portrait fall off the legacy wall when you finally meet him, but if you read all his journal entries you can't help but feel bad for him risking it all for nothing when it is revealed that the king stole the reward for himself and bankrupted the kingdom in the process. At worst Johannes is an Anti-Villain, but he could even be considered a Tragic Hero that killed the king only out of anger due to his wretched betrayal.
Awesome Music: All the music is good, but special mention goes to "Narwhal", the music playing in the Maya, which itself is surpassed by "Lamprey", the music for the boss fight of the Maya.
Again for Fridge Logic: it makes sense for Charon to always be in front of the castle, since he's a psychopomp and all that, but what about the Smith, the Enchantress and the Architect? Are they immortal? Are they descendents of a long line of identical people? Are they personifications of their jobs?
Game Breaker: As a roguelike, a few of these are to be expected.
Dragons with Dwarfism. Combine the usual tiny hitbox with a ranged attack that does not scale down with Dwarfism and infinite flight...
Before it was patched so they couldn't obtain it, Spellswords with the Time Stop spell. Stop time, then hit nearby enemies to recover lost mana. Watch as the game instantly becomes a joke, especially the boss fights.
Even without the above strategy, Spellswords in general are very useful. The amount of mana that you receive per hit is quite high, and the upgraded versions can cast larger versions of existing spells. A Spellsword with Flame Barrier or a Chakram can make short work of most enemies and all of the bosses.
Goddamn Bats: The Fireball type enemies (Charite, Pyrite, Infernite) fall with just a swing or two, but they are a pain in the butt because they constantly move around the area, making them hard to strike.
The Eyeball type enemies (Scout, Pupil, Visionary) are also weak but their projectiles track your position and they pass through all obstacles. Pupil and Visionary in particular fire a stream of projectiles.
Khidr, the first boss of the game, is a pretty good introduction to what you're in for. His attacks could put Touhou to shame in terms of Bullet Hell, and dodging is next to impossible since he takes up more than half the screen.
And then the December 2013 update brought us Neo Khidr. Take the original Khidr, make his bullets twice as fast and twice as strong, give his arena even less room to maneuver and dodge, and finally, imagine having to use a preset Spellsword every time you challenge it. Have fun.
Alexander the IV is absolutely horrible. Was the original Alexander not annoying enough? Try fighting him in a tight spike-filled chamber on two tiny platforms, segregated by a wall of spikes! This is all on top of the massive amount of Angers, which turns it into miserable Bullet Hell. In addition, you're stuck with a Hokage that dies in three hits. The final boss is nowhere near as awful as this.