Well, time to show how much of a fanboy I am...
...Dark Souls, Dragon's Dogma and Monster Hunter.
I'll start with Dragon's Dogma because there's only really one thing to say about this: Climbing on enemies. They could easily have not had this option and left combat at that, but instead, no, you get to attack weak points directly without the need for any contrived vulnerability attacks (which some other games have to use to actually get the weak point in range, and which this game does sometimes...but anyway), leading to such great mechanics as disabling a chimera head by head and cutting off a cyclops' armour then stabbing it in the eye. Magnificent. Also, boss battles generally aren't scripted, you get get sprung by them every so often, which adds a bit of immediacy, and since they're just lying around the map, you can essentially choose your own difficulty as well. EDIT: Although the metal golem is ridiculous if you're not a ranger/strider and your pawns aren't very bright, and the online Ur-Dragon is just maddening and counteracts everything you thought you knew about being able to experiment with stats. If you haven't been stacking attack or magic attack, you'll be ineffectual against the bastard.
Dark Souls just has solid bosses that are a pleasure to fight, that's all. Sadly it falls down in co-op because the boss just targets the last player who hit it/approached it, and leads to some fail AI moments and some attacks that can't figure out who they're aimed at, but in singleplayer, dodging attacks at the right time is crucial, and O&S solo will take you to the limit. Also unfortunate, Bed of Chaos is a bit of a gimmick. The tail-chopping isn't good enough for me to like either though. Actually, no, pretend I erased this section, this isn't amazing boss territory here, this is good bosses.
Monster Hunter is basically back-to-back bosses, nearly every mission has a boss-like monster in it and the ones that don't are fetch quests to get you acquainted with the map. The reason it does bosses well is because that is the entire game. They all have ecology behind them, and all have behaviours like switching areas, limping, and resting. What's more, there are a variety of breakable/cuttable parts including head crests, wings, tails, armour plating, shells and claws that not only effect how the monster behaves, but give related items at the end of the mission or when you carve the thing you've cut off, which is a lot better than random drops because it allows you to influence what you get in accordance with what you need. You can also opt to tranquilise the monster instead, which gives more items but requires more attention. Ultimately, the monsters get predictable, and as your monster-themed weapons get more powerful earlier monsters become a joke, but it still feels more like fighting a sentient thing than a lot of other games I've played. Another disadvantage is that elemental resistances can't always be intuited from the monster, especially with the colour-swapped versions, which often have different resistances, sometimes for no real reason. For example, the three Rathalos' are all weak to different things. But overall the fights feel like you're hunting a monster that knows what is happening and reacts. The music's intense as well.
I also feel like I have to say something about Bayonetta. While I did enjoy the boss battles, and the music and everything else, it still felt a bit shallow as far as the combat, but my main gripe is that I never like quicktime events. Ever. Not even 'done well', which I haven't yet seen in my opinion. The lipstick bullet thing was actually pretty good, although I don't think I should have had to redo the battle for screwing it up, but that's a nice use of the motion controls. In fact I'd say about the only nice uses of PS3 motion controls so far have been controlling a projectile. But yeah, they just weren't particularly threatening and I hate QTEs.
