NOTE: Before any niggling arguments about definitions start, let's consider "Independent Movie" to mean a movie made, post-late 70s, without the help of a major studio.
The plotting may be ripped off, but the script is not only inspired, but highly original. Reminiscent of caper movies while establishing a unique identity of its own. Bushemi's role is the best he'll ever have in his career. Same goes for Roth and Madsen. Maybe even Tierney and Penn, although it'd be debatable for those two. The movie contains multiple scenes that have had homages and parodies based off of them. Some of the dialogue in the movie is downright classic. The movie is eminently rewatchable, and the out-of-order storytelling has only been done better in one movie -- and Tarantino made that one, too.
It's hilarious and dramatic, it's got acting chops and clever shooting behind it, it's probably Tarantino's best movie from a punchy perspective. How can it not be the best independent movie?