Bve is pretty fun. I only use for the NYCT routes, the A to Lefferts is very good, nice graphics, good sounds, so is the 2 line, though last time I checked it's only available from Flatbush to 42nd Street Times Square. It's not nearly as good as MSTS though. BVE is fun if you just want to play around and pretend you drive the NYC Subway, there isn't any traffic on any of the other tracks, so you always get clear signals, no one-shot or two-shot timers either.
I've never used it for anything else besides NYCT stuff so my experience isn't that broad in terms of the other add-ons that go with it.