Apocalypse on the PS1 is a cool action game from Neversoft starring Bruce Willis. It's violent, has fun weapons, cool changes in camera perspective, great one liners, and an interesting control scheme. Its engine would later be used for Tony Hawk's Pro Skater and Spider-Man
The Sexy Brutale - A really good puzzle/stealth game with a macabre tone and memorable characters. This one's a masterpiece and I can't recommend it highly enough. Try to play it spoiler free for the best experience
The Deception series has some of the most unique gameplay I have ever seen where you play as an antagonist (who always seem to be female) killing heroes and innocent people in hilarious and violent ways using traps. The storylines usually are pretty dark and supernatural. It's like horror meets Home Alone.
Evil Dead Regeneration - A really fun Evil Dead game. It's way better than that Ash vs Evil Dead game that came out recently. I haven't played Fistful of Broomstick, but some people like that one too
The Red Star fuses shooter and brawler gameplay together. It's challenging but always fair. Some people call it a beat 'em up, but it goes into bullet hell shooter territory with a lot of the boss fights. It has two characters with distinct play styles, co-op, and an unlockable third character with yet another completely different play style.
Three Dirty Dwarves - A very unique beat 'em up with a novel story, unique art style, and a GREAT soundtrack
A King's Tale Final Fantasy XV is a fun little beat 'em up that I never hear people talk about. It plays and controls well and makes good use of well known FF enemies.
The Dishwasher Vampire Smile is one of the best 2d beat 'em up/hack and slash games I've ever played. It's very dark, surreal, and violent. The action is fast and challenging, almost feels like a 2d equivalent to modern Ninja Gaiden games. It's actually a sequel, the first game was harder. This one feels more balanced and fair. If you're familiar with the Salt and Sanctuary games, this came from the same developer
Spy Hunter should be familiar to retro gamers. The 2001 game is an awesome vehicular action game and way better than the original arcade game IMO