Overall, Homestuck's music is roughly Chiptunes meets Jazz meets Rock meets Techno, but given that there are a number of albums, I'll judge each on their own merits:
Vol 1: It's a nice and relaxing album, and it's really a simple album that does repeat tracks a bit, but in a good way. It just feels like a beginning album, and it suits it well.
Vol 2: This is probably the blandest album. There's not really a bunch of music, and most of it is remixed in an odd way. A few tracks stand out, but I'd say only get it if you're buying the whole set, otherwise just buy them and ignore everything else.
Vol 3: Much the same as Vol 2. However the songs stand out a bit more, and it's generally a nice album, albeit mostly remixed.
Vol 4: A good solid album, and sometimes considered the best album.
Vol 5: Very contentious. On the bad side, there's dozens of remixes, especially of Doctor and Endless Climb, and some of the new songs flop hard. On the good side, there is a lot of good music here, especially relistening to them. The price is also a good deal, for as many songs as it is.
Vol 6: Again, a bit contentious. Some of the songs are just downright bland, Blackest Heart in particular. However, most of the songs are really well done. However, the price on this album is a bit more unreasonable, as 10 dollars for 21 songs is more harsh than 14 for 65. YMMV, imo it's worth it.
Midnight Crew: Drawing Dead: The only side album largely praised. It's cheap, has a lot of variety in style, and is just overall nice. Jazz enthusiasts though might be turned away by the midi instruments, which are noticeable.
Alternia: Alternia is a number of things, and there are bunches of different styles that go into it. However, it's organized oddly, some of the songs are innapropriate for characters, and it killed the prospect of a team made Troll album. YMMV.
Squiddles!: By far and away, the worst album. It's a drastically different style, with a number of cheery vocal songs. A few of the instrumentals are nice, but overall it is just not worth it.
The Felt: This one is kind of a toss up. Best advice is to just listen to it and decide on your own merits if you like it. It has it's fans, but most others just can't get into it.
Homestuck For The Holidays: Christmas music. Generally good, once you get rid of the flimsy attempt at narration and cohesion.
Music Chiptunes to jazz to jazz chiptunes
Overall, Homestuck's music is roughly Chiptunes meets Jazz meets Rock meets Techno, but given that there are a number of albums, I'll judge each on their own merits: