I second Fight'N Rage and Streets of Rage 4. They have characters with depth and offer a ton of extra content.
The Streets of Rage 4 DLC "Mr. X Nightmare" adds 3 new character (Estel, Max, Shiva) and a "Survival Mode" which can keep you busy.
Guacamelee 1 (
Steam)
Yeah, I know it's a Metroidvania. But you fight enemies with melee in this game. Unlike many other 2D games which tried the formula, combat in Guacamelee feels super satisfying.
The sense of progression is good, thanks to the new moves/areas you unlock regularly. My only regret is that the last level was a real pain.
Guacamelee received an update at some point, called "
Guacamelee! Super Turbo Championship Edition"^^ which added new levels/moves/enemies and a lot of tweaks.
And seriously, a game where you can play a Luchador or turn into a chicken? What's not to love?
Fist Puncher (
Steam)
Despite its flaws, I like Fist Puncher. It's a 2D beat'em up which visuals reminds me of Renegade and Double Dragon.
This is a beat'em up with a lot of humor. They're quite a few 80s pop culture references which put a smile on my face.
Like the mission where I had to deal with a zombie-infested town or when I had to fight those naked people on a nudist camp.
The games offers 19 characters to play but you start with 7. You can develop their skills with the xp you earn.
Sadly that xp in not shared between characters, so Fist Puncher is a grindy game.
Lots of secrets too. Finally the official trailer reminds me of the Rocky IV OST: