Tank:
This is the first post where I think Alexandre is too negative.
By class size, It sounds like you mean the size of your class (freshman, sophmore, etc) rather than the size of specific courses.
Michigan is big and there is really not a lot of personal attention unless you are self motivated and seek it out. However, as a major research university with outstanding graduate programs, there are plenty of resources that are open to whomever is interested.
One example is the Hopwood Program
http://www.lsa.umich.edu/english/hopwood/default.asp . It has an amazing history and tradition.
http://www.umich.edu/pres/speeches/060421hopwood.html
I am simply listing this as an example. There are a number of programs and resources in other fields.
Most of what's great tends to be specialized, so there is less of a sense of a shared undergraduate experience then some smaller LAC schools. I hope you can find what you are looking for. Best of luck.