I watched the film, and yes I thought it was crap. But will you?
I thought the film Vampires Suck was really crap, of the 300 or so DVD's I have the worst by far is The Blair Witch Project. The sounds effects are a joke, at one point the girl is using the camera saying who is on the trip with her and she shows herself sat with the two guys, and the 'F' word is said 73 times. Thing is, I still want to have a copy of the film. But you might like that film.
So should you get the Buffy movie? Yeah, why not. I wouldn't recommend paying too much for it though.
If you take a harsh look at the series, it has many faults. Bad acting abounds, some pathetic attempts at doing sound effects, times when the continuity fails. Yet you still like it, so could you like the film even though it has several flaws?
Should a thread start where a comparison between Kristy Swanson and Sarah Michelle-Gellar is asked, if you have the film you can contribute.
And after all has been said and done, I'd recommend that you get the film.