Those who are critical of Asimov's Foundation series should remember that when it was written the field was rather young. Also that Asimov was rather young. Those who find it perhaps cliche-ridden should recognize it as the source of some of the cliches.
When science fiction writers have been asked about their favorite series work many, if not most cite "Foundation". The series needs no defense from me but since it's a work from the forties that remains in print to this day, well, that ought to speak for itself.
(Dismounts from soapbox.)
Those interested in more contemporary SF that gets both the technology and the people right are advised to pick up some Robert J. Sawyer.
Those are not my criticisms of Foundation, personally, and while I cannot presume to know others' criticisms of the series, no one has yet faulted it for being cliched, and I think we are all well aware of when it was written and its (and Asimov's) subsequent influence on the genre.
I am critical of it because it sucks.
I read it when I was about 13. Enjoyed it. When I read it again in my twenties is was a bit dry, boring and the lack of characterization made it a bit flat.