Some of it has dated, other stuff, like Life of Brian, is still superb. In fact I’d say LoB is easily the funniest film ever made.
The thing to remember though is to try and judge it by the standards of when it was made and don’t judge them against modern comedy. They broke all sorts of new ground with much of their material.
I saw them at the O2 in the summer and thought they were brilliant, not because they were funny per se, but because they were Monty Python. I never thought I’d get to see my childhood comedy heroes playing live, so for me it was almost as much emotional as anything else. I’m quite aware they said they were doing it for the money, but I suspect they were being somewhat disingenuous in that brilliant Python way. The amount of thought and effort that went into the O2 show was not just about five guys making a quick buck.