multiplayer isn't worth it on the PC...the community is way too small...i basically stopped playing after 2 weeks. no host migration means that if the host quits or gets dc'd, games over. it's so small that when i stoppped playing, i was 38 on the leaderboards.
sp is worth $37. it's too short imo but still good. i probably won't ever play it again as i was able to beat it twice over 2 days (1 sitting).