What if Robert Altman did Clue? Well, you would get this--an undeniably fascinating if somewhat unaccessible film.

A bunch of rich folk attend the hunting party of Sir William McCordle. Among the guests--the Stockbridges (he's deaf and aloof, she's, um, well something), the Merediths (he's short and aloof, she's, um, well something), the Nesbitts (he's a jerk, she married above her class, which is a no-no), the actor Ivor Novello, Hollywood producer Morris Weissman, and Maggie Smith playing her patented loveable old snob role. There's more too. All of these characters bring servants with their own personalities and there's a whole horde of servants already there with their own quirks.

What fun there is comes from the witty dialogue that occasionally hits bon mot explosion (particularly from Maggie Smith and Stephen Fry), the fluid and smooth performances (it feels like you're watching a real extended family), and the wonderful eye for the period (what a cool-looking house).

The film goes on too long though (and I wasn't interested, actually, in who did it after a while) and there are a lot of extraneous characters (the key offenders here are probably the Merediths, although the Nesbitts tend to fall into soap opera territory even more). It's fun, though, watching the British Character Actors Convention 2001 even if I can't keep some characters straight:

*To wit, Rupert, Jeremy Blond, Commander Meredith, Freddie Nesbitt, and their various wives are difficult to keep straight.
*From a certain angle, the servant George looks a lot like the servant Robert (this is annoying because Robert is a main character; George really isn't).

What is alternately interesting/annoying is that Altman shows little concern about making a movie; dialogue is whispered, mumbled, overlapped, and spoken in accents. Characters come and go (and nobody has an opening speech like "Ah, Mr. So and So and you are ___"--you have to pay attention) and plots are deliberately unresolved (most of them are).

Give it a try, I guess, but don't watch expecting a comedy or a mystery or a drama.

On second viewing, the movie is a far superior occasion because instead of trying to figure out the plot, you can enjoy more of the dialogue and the subplots. For instance, I didn't pick up on the fact that Meredith's servant hates his employer until I watched it the second time.

I believe the whole point of the film was its character studies and interactions, as well as its portrayal of class... the murder was actually secondary (or even tertiary) to the film.
Overall, I enjoyed this film, as well as the many character actors that appeared in it.

...And I just picked up the special edition dvd for only two bucks at a grocery store that was getting rid of its movies nobody rents! (I don't think that's as bad a reflection of the movie as it is of the type of movie-going crowd around here, but like MikeC said, the movie is somewhat unaccessible.)
I hadn't planned on buying this dvd until it went on sale (I never buy dvd's at full price), but I couldn't go wrong for this price. It includes some interesting deleted scenes and mini-documentaries, and a not-too-enlightening cast & crew press conference.

I watched the movie for the third time and it's interesting to pick up more and more details that I really didn't notice the first time.

The film is almost impeccably cast--as some have pointed out, this is a film where Derek Jacobi and Richard E. Grant are like fourteenth and fifteenth billed and Charles Dance basically sits around looking glum.

I think there are a few too many subplots for the film's good--for instance, I have yet to figure out the significance of the butler being a conscientious objector. The arrival of Isobel's suitor, Rupert (and his creepy friend), is incredibly undeveloped.

The ending is good, one of those "everything is different but the same" sort of endings. Some characters were static (Freddie is now sucking up to Meredith, not Sir William), others have changed (Meredith has discovered confidence).