As you play, you'll complete stages and the entire skin will change. This has an impact on the music (including its tempo), as well as the entire look of the blocks, the background, and so on. Unlocking these different audiovisual styles is the most rewarding part of Lumines, as some of them are pretty spectacular. If you've played the games before, you'll probably recognize some of the skins used here, though Supernova does have some new ones, as well.
In addition to just playing through and unlocking skins, the game also has a time attack mode, a playlist mode that lets you set up which skins you want to play, puzzle and mission modes, and so on. New to Supernova is a mode called Dig Down, where you have to clear away blocks to empty out a set number of columns before proceeding to the next, more-difficult level. There's also a sequencer that lets you piece together your own background music for a somewhat-custom skin. You'll assemble a 32-bar loop out of prefab bits and pieces of drums, basslines, and so on. When I heard that there was going to be a sequencer in the game, I got all excited. But the reliance on prefab pieces, while easy to use, doesn't give it enough range.
While I think that anyone with a reasonable level of interest in puzzle or rhythm games should absolutely own Lumines, there's really no good reason to collect them all. If you've somehow managed to dodge the series until now, Supernova's a fine place to start. But as someone that's been playing it since it was originally released on the PSP in Japan, I got tired of it almost immediately.