I can't say I've played very many games with actually satisfying melee combat. Usually it's fun at best but not satisfying. Among the games I've played, Sekiro is probably a clear winner, although it's been a while since I played it, so my memory could fail me. Still, I think it felt impactful in a way no other games I've played did, so it seems like an easy winner. Another game I think had somewhat satisying melee combat is Ghost of Tsushima, but it was to a lesser extent, and the game probably greatly benefitted from the starting sequence for many battles feeling very impactful.

Overall, I feel like melee combat is pretty hard to get to feel satisfying, or at least many popular games utterly fail at it. Usually it's just fun or interesting enough but rarely actually satisfying.

Killer Instinct.

One of my absolute favourites is Red Steel 2. It's motion-plus-powered swordplay felt incredible, using my own movements to hack, slash, block, and parry my way through hordes of enemies had a level of tactile satisfaction virtually no other game can rival.

Platinum's games like Bayonetta 1-3, Nier Automata, and Astral Chain are also fantastic thanks to how smooth and free flowing they are and the punchy audio-visual feedback of each hit.

Batman: Arkham series,

Severance: Blade of Darkness - sort of Souls before Souls (from 2001), with more precise and demanding combat, where well timed and executed hit can chop off head, arm or leg.

Exanima - physics based isometric RPG, with both single player story and arena mode - steep learning curve, given that mouse controls your actual swings, but extremely satisfying when mastered.

Hellish Quart - physics based sword fighting duel simulator of the sorts, set in 17th century Poland, so lot of sabers, though there are lot of other swords as well as some other weapons. Has HEMA scoring mode as well.

Blade & Sorcery - VR physics based combat (melee, ranged and magic) with vast amount of weapons and shields when it comes to melee - I haven't tried more recent game, but I think this is still probably best VR has to offer when it comes to melee combat, mechanics-wise.

The best melee experiences I ever had were in a little known MP game called War of the Vikings. While similar mechanically to other pc medieval combat games, two features made it feel better than any other: lunging and special moves. Lunges and quicksteps made the footsie battle much more natural and dynamic than the stiff one speed affair you see in basically every other game and the special power moves each class could execute made for the most satisfying kills ever; they were so crunchy and visceral. Taking on and beating multiple enemies at once through superior skill and daring was so very satisfying in that game. Runner up Mordhau for being the best tuned of the more traditional medieval fighters. Good fun.

For unarmed combat, gotta give it to the Fight Night and Virtua Fighter series. Can't wait for 6!

Not exactly combat you can take part in, but what Link does to Ganon at the end of Ocarina of Time:

Idk if it's my definitive most satisfying, but Ghostrunner 2 is definitely up there! The fast paced movement makes the first person melee combat all that much more exciting. With a greater emphasis on the player establishing their playstyle, it just makes the melee combat in this game so insanely good.