The IMDB Top 250 is commonly criticized for many reasons.
Chief among them is the fact that a movie's placement on the list usually comes down to the popular vote. Bigger blockbusters have a wider reach, and a wider reach can mean more people are rating highly, regardless of film quality.
And while the list should in no way be considered as representing the 250 finest films ever made (for the aforementioned reason), isn't it also useless as a ranking system when people can rate films without even seeing them, or give a film ten out of ten/one out of ten numerous times via numerous different user accounts?
However, this system does have one advantage. Since a good chunk of IMDB voters are only interested in seeing their favourite blockbuster rise to the top by giving it a ten out of ten, or seeing a rival blockbuster sink by giving it a one out of ten, smaller films often go overlooked, and that means their ratings are usually honest.
So when a smaller, lesser-known film does enter the IMDB Top 250, you can be fairly confident that its high rating is genuinely reflective of its quality. And they're the ones that most deserve your time...