Quatermass meets Assault on Precinct 13 makes for a much more interesting concept than the film delivers unfortunately. There's a good movie in there, but stuff is bungled. Characters are built up but dispatched without fanfare. The flashback structure dissipates rather than adds to the suspense.
Good score from Carpenter + Anthrax. Courtney Love was originally cast as the lead with Henstridge taking over at the last minute.