I've been playing a lot of Beat Hazard in the past couple of days, ever since the ticket challenge for it went up. It was a good excuse to get back into the game.
It's one of those games where you 'play your music', this time based around a shoot-em-up (shmup for short). The difficulty of the level depends on the song you put in. Generally, a slow, lighter song will get you an easier level and a faster, harder song a more difficult one. It's quite fun to see the levels your songs produce and get ever-higher scores thanks to visual intensity (50% - 200%) and various difficulty levels (Easy, Normal, Hardcore, Insane and Suicidal). It does suffer a little from having no real way to compare scores for your song with other people - there are just leaderboards for song length. There's no real excuse for not having it; Audiosurf did, and that was the first 'play your music' game, as far as I'm aware.
Towards the end of my playing experience, I reached Elite, and decided that then would be a great time to grab the DLC, Beat Hazard Ultra, especially since it was still on sale. The DLC includes online co-op/competitive play, a boss rush mode, more types of enemies and super weapons. I have to say, I don't like the game as much with it. It's a lot more busy, in a bad way, as instead of focusing on dodging and firing at stuff, there's now enemies that require different tactics other than focusing your shot at them or bomb spamming. It breaks up the flow, and the levels don't feel as natural.
I've reached the max level and played it for more than 5 hours, so I'm chalking this one down as a :B:. It's got 4/5 stars, but I don't think I'll go back much, if ever. There are better shmups and what appeal the game had was broken for me by buying Ultra. It's a shame, because before then, I could have seen myself getting a :C: for it. Ah well, you live and learn.