Northwestern is a great, great school. It is a Big 10 school which has a enormous impact on its social life. If you are used to the trappings and attitudes of London, you won’t find that culture in a Midwestern suburb.
If you are interested because of Chicago and winter is an issue, temper your enthusiasm. Winter in Hanover and Ithaca will be much more fun with many, many things to do.
Also, figure 90 minutes each way to Chicago on the weekend on the train. I think you will find that students going to Chicago on the weekends is actually pretty rare. Roughly half of the students receive need based financial aid, so many won’t have the cash to party in Chicago. Even the students not receiving financial aid won’t be in a position to socialize in Chicago very much.