Despite the fact this movie is so factually incorrect and utterly removed from reality as to basically be 99% fiction, I still have always really liked it. This and Repo Man are probably the only Alex Cox films I will willingly watch.
Lydon deconstructs the movie pretty well in his autobiography and the original commentary track for the Criterion DVD features many people who actually knew and worked with the Pistols and all they talk about is how historically inaccurate the whole thing is down to even the most "how could you get that wrong?" details.
Alex Cox is a very self-absorbed idiot, he really is. But, on occasion, he is a good filmmaker. Just misguided in certain ways really.