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.
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.
Complete Monster: To sate his desire for immortality, the king not only willingly emptied his royal coffers (possibly destroying the economy), but he also sacrificed his family members in order to get to the fountain of youth.
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.