I think the traffic depends on your route. I had an 11 mile drive to campus, and there were a few times it took 45 minutes. That's pretty crappy. The biggest issue is that all cars going into and out of Bozeman must pass through one of two intersections. I live in Seattle now, and I won't lie and say its better, but there are times of day when 12 miles takes you 15 minutes, others when it takes you an hour.
MSU, what to say. I can't really bad mouth it. I got a degree and a good job ... that was the plan. The College of Engineering had a few, er several, down years, but I believe they are on the rebound. And some large companies, like Boeing, still have a lot of MSU alums. I found that is an important aspect in your future success. Its reasonably priced, or was at least. I think those tuition increases were getting pretty ridiculous. I never lived in the dorms, so I can't help you out there. But make a lot of friends, knowing people that go to house parties is key until you're 21. Also, the guy/girl ratio, or guy/hot girl ratio is pretty dismal. Be prepared for some mistakes of desperation.
Bridger was starting to get waaaaaaaaay too overcrowded when I left. When I was in high school, they only had half the parking lots they do know. Having Shlasman's open now made a big difference, the couple times I've been back. I recall powder days when the Ridge would be completely tracked by 10. I might have skied Big Sky more, but the drive was a bit much and all my friends wanted to ski Bridger. Also, I'm scared of the militant a-hole "locals" at Big Sky. I can't stand those jackasses that moved to Big Sky a couple years ago and now think they own the place.
I lived in there from age 4 to age 22. By the end the only thing I liked was my friends. It can be a fun place for a few years, but that long of a time there just wasn't for me. I was bored by the end. I was sick of the Californians and Sierra Club coming in and telling us how to live. I was sick of the overcrowding of a city, but not having the amenities to make up for it. I was sick of bumping into people I knew but didn't want to talk to, everywhere I went. I was sick of the hicks, hippies and white trash.
Your mileage may vary, but I was ready to get out of there. That being said, I like visiting Bozeman now.