This short review contains no spoilers, except the fact that the movie is about time travel, and now I've just spoiled that for you anyway. Whoops.
Bender's Big Score is the first, and probably the best, of the four feature length Futurama films that represented either the last gasp of the original production run or the first breath of the second, depending on your perspective. Unlike many other film adaptations of television series, the formula is not substantially different than that used in single episodes - quite the contrary, the film is something of a medley of everything that made the series fun to watch, complete with several musical numbers and cameo inclusions of nearly every bit character from the entire first production run and the usual full complement of fourth-wall breaking moments. The extra time simply allows for a more involved plot.
...a much more involved plot.
Bender: "Geesh, this is confusing..."
The Futurama series' entire subtextual plot driver had been time travel, in one form or another; in the very first episode Fry, apparently a contemporary everyman, "travels" to the future via cryogenics - and most of the major story arc developments thereafter invoked time travel in some form or other as well. Notably, Fry becomes his own grandfather in "Roswell That Ends Well", and travels back in time again (this time on purpose) in "The Why of Fry". In Bender's Big Score however, time travel - honest-to-god, Back-To-The-Future-style time machine time travel - is introduced for the first time; not only introduced, but made the focus of the plot, generally considered a risky move in sci-fi circles. Fortunately it works well - naturally, this being Futurama, every sci-fi time travel trope in the book is mercilessly dragged out, parodied, and roundly deconstructed. While the time travel model used in the film is not exactly "hard sci-fi" (the so-called "paradox correcting" time machine is in fact nothing of the sort), it is tuned for maximum comedy, so it's hard to criticise it on that account.
Bender: (looking directly at the camera) "...and I bet it’s going to get a lot more confusing!"
Bender's Big Score has an extremely tangled timeline, but while it is sometimes compared to Primer in this respect, it is not nearly as difficult to follow: everyone's *personal* timeline is pretty much followed in a linear fashion. Integrating all the various scenes into a coherent whole still takes some effort, and for my part it required multiple viewings to properly understand it. A lot of thought and inventiveness was clearly poured in.
The scale of the plot is sufficiently epic, and the implementation of it sufficiently engaging, to more than make up for the lack of dense laugh-a-minute jokes (which is to be expected anyway when a plot has to be sustained over that length of time). Unfortunately, the requirement that the film be divided into 3 episode length portions for television broadcast, while invisible to the DVD viewer, leads to some moderate pacing issues - it's a little too easy to get bored about 3/4 of the way through. Nevertheless, at no point does it lose its way - events lead, if not logically or even serially, then at least haphazardly in the general direction of a reasonably dramatic climax, and the end of the film leaves one with a satisfying feeling of a story well-told (coupled with a distinct sense of "what the fuck just happened").
I'll leave more detailed analysis to others more skilled, but my verdict stands at:
A--