I finally 100%ed Retro/Grade. Great game.
Retro/Grade is a reverse shmup rythm game. This means you are going back in time undoing every shot you fired. Now you know why it didn't sell too much, two niche genres put together but quite good at that.
From the right side you have the notes you need to press while from the right side come the laser shots that go back to their point of origin, so you need to pay attention to to both sides of the screen at all times. The game has 6 difficulties and just like any guitar hero game more notes and lanes are added when changing them. You also have a reverse mechanic to go back in time (or forward

) and get the notes right and erase any mistake you made, but this is limited.
The campaign consists of only 10 tracks and even though they are good a few more songs would have been nice.
Another thing that is a little hard to get used to is the vibrant colors, specially when you are in overdrive mode, making you lose track of the notes you need to press or the enemy fire you need to avoid. But once you memorize the songs it all comes down to deciding when to activate it to increase you score.
Finally the game has another campaign which consists of lots of challenges. While you play the same songs again, sometimes you need to do so without mistakes or lane coloring, with the camera zoomed in, mirror world or at a faster speed, or all of them at once. As you beat this challenges you can unlock new ships, artwork and the music player.
On the good side, you can play the game not only with a keyboard and gamepad but with a compatible GH guitar as well. I beat it using mostly the 360 gamepad but changed to a DS3 on the last levels. I recommend using the latter for the superior D-pad.
Like any music/rythm game your enjoyment depends if you like the music, so if you do I would at least give it a chance.
I bought the game during the summer sale and I got 50 hours out of it, so I can not complain.