ES4 has a decent combat and MMM makes it a lot more alive and interesting, but the truth is that very few games in the industry managed to implement a really good combat system or unique boss fights. Pillars of Eternity I and II had really (I mean reeeally) good combat systems. Dragon's Dogma had the best single player game open world game's combat I've found but wasn't a very good game (storywise). Other than that, FF8 had cool spells and enemy strategies but the leveling system is fundamentally broken. FF14 on the other hand excelled at making challenging and different boss fights. The bosses had several AI/Attack "phases" and AoE attacks. Depending on the magnitude of the attack, they could one shot you. Other than those I can think of no other game that managed to do an exciting hack and slash combat (take FF8 away from the list, it's not hack and slash).
s***. Hack and slash is only fun til a certain degree. Imo the ideal game fight is one that makes you think a lot.
For example, here's a nice but simple rule for Oblivion who would screw most barbaric classes: you cannot regenerate magicka in combat unless you chose a magic class during character creation. So if you've mastered restoration as a warrior you'll still die. And if you're a mage, you can't have any armor defenses but your magicka regenerates pretty quickly. Here's another one: all weapon attacks have a high chance of missing and a small chance of dealing double damage during a critical strike. Missing attacks can be mitigated to 5-10% if you're a Blade/Blunt expert or master. Unblocked arrows that pierce your unprotected head/face have a 99% of chance of instantly killing you. If you don't die, you'll faint and be teleported to a cathedral where the priests will heal your injuries. Archers would be literal Terror under these new rules and they would aim for your head whenever possible haheahehae. Master acrobats can briefly slow time do efficiently dodge lower level enemies, and acrobat masters can avoid most of your attacks as well unless you're also a master. These are basic RPG limits but they would enhance oblivion's gameplay I think.
Skyrim's combat is even more bland than Oblivion's. You can't even choose a specific class and once you master every skill just hit the attack button and you should be totally fine.
RPGs combat mechanics need to learn more from PoE and Final Fantasy and less from Bethesda. Anyone knows of other games with good/complex combat systems that actually makes you think in order to defeat enemies?