you're getting some good feedback from sankd, but i figured i'd add my two cents.
i've spent a little time in Mount Pleasant and on CMU's campus a few different times, over the last 15 years or so, and my first answer is, it's a lot like any place in Michigan with under 30,000 people in it. (got that from city-data.) what i mean is, it's big enough that the place is self-sufficient - you don't have to go 50 miles to buy an appliance, or furniture or something - but it doesn't have any of the characteristics of a big city. good or bad. as was already mentioned, if you drive out of town, after not long in any direction it's just farm land. the casino is a plus for some people, but i don't care much for it. as for where to live, i have no specific intel - but most places like this in MI run the same way; there's definitely a student ghetto somewhere, i'm sure there are terrible over-priced student apartments somewhere, and the real rent deals are probably found in single-family dwellings a bit away from campus. this is the sort of place that's suffered from foreclosures and falling home prices, so with a little work on your part you can probably find a steal, if you're willing to live in a slightly shabby (but not at all dangerous) family neighborhood.
two things to keep in mind about Mount Pleasant: one, there are as many students at CMU as there are residents of the city, which partly means a lot of students technically live in a neighboring township or commute to campus, but also means the university is THE defining presence in the city. two, i can't speak to the bus system, which is probably small but serviceable, but you will not be able to go ANYWHERE outside MP without a CAR, or a friend with a car. Michigan operates on cars. there's no reasonably-prices intercity transport anywhere in the state.
finally, i really like the campus.