The first season/most of season two is very creature of the week, obviously better than Buffy's first season, but it wouldn't change your world or anything. The best episodes from these seasons are not surprisingly the ones where Spike, Buffy and Faith, etc. come over.
From season 3 on you get really good season-long (or multi-season) arcs that are pretty great, imo. Its last season and finale are definitely better than Buffy's, possibly because they didn't know till well late that the show had been cancelled. Angel as a character kicks much more ass on his own show, chucking baddies out of of skyscraper windows and stuff. There's considerably less brooding. Without the fun side characters though it would probably sink fast. There's even a funny singing demon sidekick who's dead in real life now
Anyway, I'd definitely watch it once.