It's popular because it was paired with Cowboy Bebop for years.
I only watched it because of that (Bebop was the first anime I ever liked.) I hated it at first because there's a lot of retarded comedy, but it grew on me and halfway through the series it gets serious and awesome. I still love Vash.
I tried to get into the manga, I own like 6 volumes of it, but once it had nothing to do with the anime I found it absolutely impossible to follow and understand so I gave up. I was still a pretty strong fan for a year or two, but I'm not even slightly interested now.
Can't NOT wait for the fuckin movie.