Arthur and his knights encounter an ill-tempered God, who sends them on a quixotic quest for the Holy Grail. Most of the knights are eventually killed off, some by a killer rabbit, and others by an eccentric bridge keeper. Connie Booth and Carol Cleveland, both familiar from frequent minor roles in the "Monty Python" television series, show up respectively as a purported witch and a nymphomaniac convent girl.
How others will see it. Too popular to be a cult movie, Monty Python and the Holy Grail is beloved by anglophiles, fans of its predecessor television series, and by those who enjoy truly silly movies such as the Naked Gun series.
Critics were ambivalent back in 1975, but the first true Python movie (And Now For Something Completely Different was a clip job) is widely admired today. At the time of writing, it is #67 in the imdb.com Top 250, which means that its user ratings are extremely high. They do slide with advancing age, however, particularly with women (9.1/10 under 18, 8.7/10 from 18-29, 8.4/10 from 30-44, and 7.8 over 45). Presumably, silly wears thin for some over the course of 90 minutes.
How I felt about it. There are things that I liked about this movie. The music is very good. Terry Gilliam's animation is remarkable, as was the case with the classic television comedy series. (It is a shame that Gilliam has since concentrated on his career as a director, which while undoubtedly more profitable has cost us the pleasure of watching more of his surreal toons).
But most of the movie is silly low budget live action. And it is better than most such films, although far from the quality of the ultimate classic silly comedy, Never Give a Sucker an Even Break (1941).
The typical skit has one or two funny lines, and the occasional line works completely ("Oh, don't be such a baby"). More often though, even lines that are considered legendary ("Your father smelt of elderberries") are beloved principally by the nerdy set, as noted in the "Simpsons" episode "Homer Goes to College." The convent castle skit goes on too long, since even the most sexually deprived schoolgirls are more like Lolita and less like 'actresses' in a porn spanking fantasy.
The real reason, though, that the film doesn't quite work is its length. It suffers from the same problem that Pee-Wee's Big Adventure had, relative to its similar television show. The television show was chopped into unrelated sketches of two to six minutes each, an ideal format for satire. A feature must maintain continuity of plot and character, no matter how silly it may be. This greatly increases the difficulty of making it funny. The task was too much for Terry Gilliam, which is why Terry Jones took over. Inspiration gives way to perspiration. The film gets completed, but remains marginally disappointing.