Not a single mention (seemingly) for Assault Android Cactus, Downwell and Pix the Cat in this thread leaves me sad.
Assault Android Cactus (34% off)
My favourite twin-stick shooter in years because of how expertly crafted it is, regardless of it being WitchBlade's debut title. It may come off of as primarily a co-op experience (local only for what it's worth) but it carries enough meat to its bones to still be a worthwhile single player endeavour, especially when gunning for the S+ ranks per stage. For starters: although it doesn't seem that way on the surface, there is very little randomness that comes into play here, allowing for plenty of room for refinement in one's approach to a level or boss fight. The often dynamic arenas themselves can pose as big of a threat as the robot opposition (something you rarely see in a shooter of this style) with hardly any 'gimmick' recycling to boot, with the enemies simultaneously being sufficiently varied. There's 9 playable androids to choose from, nearly all of them with a noticeably different strategy yet still viable to achieve the highest ratings with. Said characters vary from someone wielding a railgun with proximinity mines on the side, someone who spews lava whilst carrying a giant fuckin' drill, someone who can only damage others through her separate robot (meaning you have to pay attention to three different things simultaneously) or someone with a chargeable vorpal blade allowing for long-distance and highly damaging dashes. The soundtrack is upbeat and compliments the frantic action nicely, there's a lot of effort put into audiovisual readability to prevent a need to constantly glance over to the HUD for crucial information, the bosses are designed around reasonable 'bullet hell' patterns without overstaying their welcome and there exist numerous EX Options (first-person camera, visual filters, upping the enemy count et cetera) for a change of pace. Several other modes too outside of the campaign, such as a Boss Rush, an Infinite Survival and a Daily Challenge.
Or just watch this
official trailer. Sure sold me when I first laid eyes on this game.
Downwell (33% off)
Fast-paced vertical rogue-lite with an ingenious combo system that balances some level of risk-reward to reap its rewards. The idea behind it is simple but with enough nuance in its underlying systems to remain engaging (especially so once you unlock Hard Mode) and its soundtrack is also composed by the same guy who was responsible for Spelunky's, so catchy tunes were all but guaranteed. Certainly one of this year's most underrated gems and besides, it's only 2 bucks right now.
Pix the Cat (75% off)
'Pac-Snake on Crack featuring cute little ducklings' ought to be a concise enough description!