Astroman is a good platformer. The physics and enemies remind me a lot of early Metroid games but the game is level-based, not open world like Metroid. There are upgrades to find but with the different structure it doesn't feel like Metroid. Still fun.
Well, let's see what else there was that didn't get mentioned yet...
radiangames everything: This guy is a machine, he's been making a game per month and they're all great.
Garden Gnome Carnage: It's hilarious, WTF and IMO worth paying the dollar for even though there's a free flash version. This one has military dudes and matching music instead of the christmas elves of the original, IMO that funnier.
Null Divide: Retro-styled (and I mean that in a NES way, not Jeff Minter) twin-stick shooter with Metroidy upgrading. It makes more use of upgrading than Astroman so it feels more Metroidy than that.
Abaddon Retribution: Nice space shooter (not purely twin-stick) where you upgrade and defend a massive mothership, the difficulty curve in coop MP is a bit wonky but otherwise it's great.
Coral's Curse: Another Metroidy game, this one has one big connected world and casts you as a snake-woman with a long tail that you have to use to get through the world. The physics make it interesting.