John Cleese had it more or less right when he walked away from Flying Circus after the first three seasons, or "series" as they call seasons over there. Python was of a particular time and place, it could only exhaust itself and achieve a point of diminishing returns before long, and anyway less is more.
Python and the Holy Grail is cheap and cheerful; it's episodic to the point of being practically glorified sketch comedy and doesn't succumb to service of a plot; it bookends the TV series, so that the Flying Circus spirit hasn't yet gone out of the Pythons; it's All-England, England being the font of comedy in the world and the sort-of infrastructure for a very great deal of Python; and most of all it's comedy for comedy's sake -- comedy first, second, and last and none of your dreadful politics or pretensions, thanks very much.
The two later Python features Life of Brian and The Meaning of Life depart from that Holy Grail formula and are disappointments for it. Life of Brian commits the comedy sin of taking itself seriously. It's politics, it's insufficiently episodic to liberate itself from its point-making plot, its setting and subject could scarcely be any less comic, and it comes too late, after the spirit had passed.
Meaning of Life is at least a compilation of sketches, but it too much presumes to be a proper movie, a big-deal feature film, it has a weightiness if not an air of menace about it which acts as a wet blanket on the fun of the TV series and Grail movie, and by the time of Meaning of Life there wasn't material or spirit enough left in the Pythons to fill a feature film. The Pythons were too old and too changed for a reprise of Flying Circus, and anyway the time for Flying Circus had come and gone.
Which is not to say there's no life after Python, only that the Pythons stayed too long at the fair. Of all the post-Python projects John Cleese's Fawlty Towers is far and away the greatest and incidentally also the proof positive for the Cleese Doctrine of less is more, that series lasting all of two seasons and 12 episodes all told. Cleese was good in Fish Called Wanda and he near enough to hijacked Cheers in his recurring role there, so outshining the rest of the show as to have diminished it in his wake. Cleese doesn't miss too many opportunities to trade on his brand, whether in Schweppes TV ads or Harry Potter cameos, etc., but he's an institution and a sort-of ambassador for Britain, and anyway he was the one Python who got it right, that the thing to do was walk away and quit while Python was ahead.
I dearly love Michael Palin's movies and travelogues post-Python, although those don't presume to be comedy proper; they're more humor than comedy per se. Graham Chapman was a hard-case drunk and died too young, of cancer. Eric Idle has inclined more than I can abide to showtunes. Terry Jones is a politician with jokes. And Terry Gilliam who really never was so much a comic as a visual artist has made of himself a leading exponent of fantastical filmmaking.
And another thing: the Pythons didn't invent comedy or TV comedy or TV sketch comedy or even British TV sketch comedy, and would never pretend to that claim themselves. Flying Circus was derivative of Spike Milligan's Q, and Milligan's Goon Show before that, and the Pythons generally were products of England and of Austerity Britain and of the good schools and of the English way of humor, which goes back further than I'm able to put a finger on.
All that said, I suppose I'm relieved in a way that the Pythons did return to the trough one time too many, or several times too many, because otherwise we might be compelled to venerate them as demigods and despair of attempting humor ourselves.
