I suggest you go to the university of York website and look at their online open days and campus tours. It is a Russel group university and one of the top unis in the country so could be considered a prestigious university although not as much as oxbridge.. They have a great campus and passionate lecturers. I don't know much about the subject you are looking at taking so you will have to wait for some other replies. Negatives i guess would be that the weather in York is completely dreadful most of the year. Expect frost, rain, hail, sleet, lots of wind, and cold... even in the summer.
Is it diverse? I guess that depends on your view of diverse. Compare it to Cornwall and its an extremely diverse bubbling broth of cultures. Compare it to London and it's extremely white. Saying that, the people are nice and the students are inclusive so you should have no problem fitting in if you are not a white brit. Why does diversity matter?