The more time I spend on IMDb's Top 250 list, the more flaws I find with it. Not that I'm ever likely to watch a dud film if I stick to the list, but I will doubtless miss many hidden gems.
I knew that IMDb doesn't include documentaries in its Top 250 (and therefore ignores such unmissable treasures as The King of Kong, The Corporation, Koyaanisqatsi, Touching the Void, Capturing the Friedmans, Man on Wire...), but what else gets excluded? Well, according to their FAQ, films with fewer than 1,300 votes, films shorter than 45 minutes and non-theatrical releases are also excluded.
Furthermore, only votes from "regular voters" are considered when calculating the weighted average rating for each film. What constitutes a regular voter is explicitly mysterious.
The following films have received over 20,000 votes on IMDb, with an average rating of 8.1 or higher (which would be more than enough to secure a place in the Top 250) - and yet they are excluded from the Top 250, presumably because fewer than 1,300 of those votes came from "regular voters".
Hayao Miyazaki's Howl's Moving Castle & My Neighbour Totoro
The Man From Earth (the only US title on this list)
Fa yeung nin wa
The Sea Inside
The 400 Blows
Two conclusions can be drawn: 1. Regular voters seem to be significantly biased against foreign (ie non-US) films. 2. Either the "regular voters" bar is set very high, or there is an awful lot of unsportsmanlike ballot-box stuffing going on.
An extended listing of the Top 500, following the same criteria, is available to IMDbPro subscribers. I wonder how many of the films mentioned above are in 251-500 - implying that "regular voters" gave them slightly less high ratings? If the answer is "not many" or "none", my conclusions become more acute.
Turkish voters deserve a special mention for being particularly zealous. With over 10,000 votes, Babam Ve Oglum has a phenomenally high score of 8.9, which would place it at least 7th on the Top 250 - but the "regular voters" obviously disagree. Gegen die Wand (score 8.1, 14,167 voters), Eskiya (8.2, 8,229), and Hababam sinifi (9.0, 5,817) are also neglected - they have cracked the Top 250 briefly in the past, but then mysteriously dropped away.