The sequel to the semi-popular flash game Soundodger on Adult Swim Games, Soundodger+ offers much more in terms of difficulty and replayability.
If you haven't already, check out the original on Adult Swim, here (it has half of the levels, and the same gameplay): http://games.adultswim.com/soundodger-puzzle-online-game.html
Though it may be easy to jump right to the level editor or auto-gen mode, Soundodger+ is mostly about its single-player experience. There are many edge-of-your-seat moments where focus and concentration are key. This may not be apparent from the first few levels or trailer; the game starts off slow, easing you into the later levels with simplified versions of the patterns; it feels a little too slow moving in, and you need to beat ~10 of these levels before the advanced levels can be played. This is my only real gripe though; the level of polish and love put into the later levels is evident in spades. (Look for advanced levels indicated by a black background.)
The quality of music is also exceptional. If you peruse the Indie section of Steam often, there's a good chance that you'll recognize some of the artists; Disasterpeace, Sonic (also known as Jasper Byrne, who did all of Lone Survivor [music too]), Austin Wintory, Danny Baranowsky, Lifeformed, and Bill Kiley. That's not to say that the others not mentioned are bad; far from it. You may recognize Ghost Kollective, but other names such as Mike Forst, D. WIGHT, Anoctave and Bean proved to be exceptional with the tracks they provided.
Next, the editor. Soundodger+ has plenty of very interesting mechanics; you can slow down and invert time, fill the screen with bullets, and control the movement of the outside "enemies." All of this can be accessed and used in the editor. Though initially appearing dense and convoluted, the editor makes a ton more sense after viewing the available online tutorials, and it can be a blast not only to play finished levels, but also to watch said levels as well. Be warned, Soundodger+ only accepts tracks encoded at 44.1 kHz; I ran into the problem of not being able to use some tracks I wanted to because of this.
Finally, the Auto-Gen mode. I put this at the bottom because it's easily the weakest part of Soundodger+. Levels are typically created on a scale of how loud the music is, similar to Audiosurf. If you don't have loud tracks, you'll end up with a level that's too easy, on the scale of the early campaign levels. The levels generated often don't make sense either; the game creates a pattern only when there's a spike in the noise, causing bullets to fire off at seemingly random times. And again, the Auto-Gen mode only works for songs encoded at 44.1 kHz, same as the editor.
TL;DR: Soundodger+ is highly recommended, especially if you're looking for something in the vein of Bit.Trip, Audiosurf, Sound Shapes or 140. Do not buy for the auto-gen; rather, buy for the single player experience.