FWWM has some of the most hideous dialogue in the whole series. It's like the most painful parts of the series with nothing to redeem it. Dear Lord, "Night time is my time" made me momentarily sympathetic for Bob. "Everything we have is everything" (or whatever) was even more absurd and useless. And then there's the intoxicated exchanges with Jacques...God, that scene felt like the worst moments of The Doors movie jammed into 10 minutes.
Not only is the dialogue hideous, but the acting is even worse. Sheryl Lee was supposed to be good in this, but she's generally over the top. The scenes with Donna are handled well. Four words sum up her acting nicely: "I LOVEEEEEE YOOUUUU JAYYYYMMESZZZZZ!!!a!1q!!?1!!!"
Leland however is, as always, a menacing and broken man, easily my favorite part of this mess. Otherwise, it's just really off. Sarah is bad, all the kids are bad (nothing new about that), and anything implied to be supernatural feels stiff and absurd rather than etheral.
The actual black lodge sequences, however, are brilliant as always, and I felt like anything with Bob was pretty nice. The problem is that there was no strong character at its center to anchor the film as we waded through those scenes, and little actual case to juxtapose them (there actually was, but the dearth of FBI scenes made it appear as if there wasn't), so we're left to join Lynch in his journey up shit creek without a paddle.
So, that added nothing of significance to the show (Annie showed up to say hi, but the end of season 2 is generally left untouched), and it actually convoluted things to no real benefit (I have even less of an idea where Cooper fits into this web, especially since the Lodges occupy a world outside of time and he was in every black lodge sequence), so I have no idea why anyone would watch this beyond experiencing a sense of completion. Sub-par acting, sub-par dialogue, pacing that slowly got worse as it proceeded, and emphasis on the wrong characters all contribute to this film being unnecessary in the context of the show and poor on its own merits.
The show is still astounding though.