I've been playing these recently and enjoying them. Keep in mind I am old, so I'm going to be recommending a lot of games that remind me of the ones I played when I was younger.

Aggelos

It's like Wonder Boy, but not. Just enough of it's own thing, and yet there's a lot of familiarity if you've ever played Wonder Boy.

https://store.steampowered.com/app/717310/Aggelos/

Crypt Stalker

More of an action platformer akin to Batman on the NES, rather than a metroidvania. But it's still fun.

https://store.steampowered.com/app/628550/Crypt_Stalker/

Door Kickers: Action Squad

Feels like a more thought out Broforce with less explosions and more of a set gameplay experience. You play as one of many Police SWAT types, and try and rescue hostages, take out baddies, as well as find and disarm the bombs. They also recently added a random mode, and a zombie mode.

https://store.steampowered.com/app/686200/Door_Kickers_Action_Squad/

Dungeons of Sundaria

It's a third or first person dungeon crawl, with loot of all different qualities to collect, sell and equip. Cautious recommend at this point. I like what's there, but it is early acess, and does need more time in the oven. They are working on it and patching it regularly, which is a good sign.

https://store.steampowered.com/app/587520/Dungeons_of_Sundaria/

Huntdown

A bit like Door Kickers, but with less tactical feel and more of a cartoon or comic-like experience. Really well drawn pixel characters too, if a bit silly sometimes. The bosses and gangs wear their inspirations on their sleeves.

https://store.steampowered.com/app/598550/HUNTDOWN/

Micro Mages

Feels like a game that would have done well if it was made for the NES back in the day. Plays a lot like ice climbers mixed with gauntlet in that you have to take out enemies and then find the exit to get to the next floor. Which means collecting power ups, bouncing off walls and using the stage layout to get to the next boss. Each boss is the 3rd stage and I believe there's 5 floors. There's also a skull difficulty which gives the enemies more abilities, different patterns and a slightly more difficult game. But it's by no means actually difficult if you're careful.

https://store.steampowered.com/app/1065020/Micro_Mages/

Oniken

A challenging game that revolves around knowing what's going to happen before it happens ala Ninja Gaiden. So there is a lot of redoing stage sections, getting attacked by annoying enemies, or just basically playing the game until you can get through it without dying. While it is tough, I'm probably making it sound harder than it is.

https://store.steampowered.com/app/252010/Oniken_Unstoppable_Edition/

Strange Brigade

You play as an Indiana Jones style character from a cast of characters going through egypt and the carribean in the 1920s as if your action adventure life was a radio serial from the really old timey ... time. I can't think of another game that does this, so it's kinda neat. The narrator, imo, never feels like he overstays his welcome.

And no, it's not really an indie title, but I'm throwing it in here because it was fun to play co-op with a friend all the way through, and it regularly goes on sale complete for under 20 canadian, and I just don't think it got the attention it deserved. I never had it crash, glitch or bug out in the 20 hours it took to get through. Which considering the AAA games that have launched since Strange Brigade came out, and the state in which they launched, is like a diamond in the rough all on it's own.

And if a co-op experience like that is not for you, they also added an arena mode where waves of enemies come at you, as well as a mercenaries from Resident Evil 4 style mode as well.

https://store.steampowered.com/app/312670/Strange_Brigade/