Electronic Super Joy was a brutal platformer full of electronic music and was, by most accounts, very good indeed: 90% of its 2,500 Steam user reviews are positive. Developer Michael Todd Games has just released a sequel that's completely free, despite having more levels than the original.
You run, double jump and smash your way through more than 55 levels, murdering bosses—including Santa Claus himself, who has started eating his reindeer—and discovering secret areas. It has a thumping soundtrack to drive you forward between checkpoints, and a handful of new abilities, including a sword that dashes you forward and an explosive jump.
Alongside the free version, you can pay $13/£10.30 for a Gold Edition. On top of the base game you'll get three bonus levels, an extra ability, a new Derpy Dragon boss fight, extra music and a full, downloadable version of the soundtrack. You may as well try out the free version first and then decide if you want the extra stuff.
The early user reviews are positive. If you've checked it out, let me know how you found it in the comments below.