During the really cold parts of the winter,the weather is often great for flying, but during the fall and spring, the weather is usually terrible, with several multiple-day stretches of low ceilings and/or icing that make flying difficult. December-February is generally decent flying weather (since it's too cold for much cloud cover or snow), but there will be a few periods (typically 1-2 days each) in those months when blizzards will shut things down.
I spent six years up there (four as a student, two as an instructor), and generally liked it and would probably do it again, but there are some drawbacks.
On the positive side, the faculty at Odegard are almost universally top notch, the instructors are generally pretty good, the airplanes are maintained in excellent condition and are much better equipped than you'll see at part 61 schools, and the gen-ed courses at UND are very solid, since UND functions as a state university that happens to have a world-class flight school attached (as opposed to the "flight school that added a college" approach Riddle takes). Campus life at UND is far more interesting than anything Riddle could provide (North Dakota actually has women!), and Grand Forks is a great place to live, although it is a small city and doesn't have a ton of things going on 24-7.
I do have issues with how UND treats their instructors, but as a student, my only complaint was that the "UND way" of doing things doesn't always carry over well to the real world (especially if you instruct somewhere else), and I think some of their safety policies go a little too far and remove some of the decision making that students need to be able to learn.
I actually looked at Riddle before coming to UND, and aside from the massive cost difference (UND is less than half the tuition, for a much better general education background, IMHO), the deciding factor to me was the attitudes of the two schools. All of the faculty I talked to at Riddle struck me as almost arrogant, and the school was selling the hell out of the "you'll go to a major airline and make big bucks!" line whenever job prospects were brought up. In contrast, the faculty I met at UND were a lot more down to earth, and they flat out told people there on a campus visit that airlines weren't a stable industry, regional pay was pretty bad, and they strongly recommended minoring (or getting a second major) in something that wasn't flying.