Yeah, someone mentioned this in the movie discussion (might even have been you) and I agree. Lots of stuff that people new to the "universe" assumed was explained or a reference to the series really wasn't. Despite the fact that there was approximately 10 hours of material that preceeded...
Depends on what you liked so much about Buffy that you didn't find in Angel. I find Firefly tonally more similar to Angel than Buffy but the fact that you are a big Buffy fan means that you should at least rent (and probably consider buying) the Firefly DVD set.