It was working fine for me earlier (about 2 hours ago, maybe 3.) Now it's having some issues. However, when I get a 502 (not uncommon for me at other times) I can refresh instantly, and it works after a few tries. I don't think it's unusable, but it helps that there's only one mod I'm downloading today. DL speed seems not unreasonable, I estimate it's around 1.3 Mb/s (considering it took 30s to DL 15% of Falskaar's ~500mb bulk.) That's a decent DL speed, although I've seen higher on Nexus.
Only the Skyrim Nexus, mind. The others I've tried are fine.