Hallowe'en in Chicago is fun, I'm sure there's TONS of events -- I can link you to some Stuff To Do In Chicago websites if you want.

Chicagoween is mostly for kids, but if you go down to see it on Daley Plaza downtown they DO have a really spectacularly hideous orange-dyed fountain. :D

O'Hare Westin isn't far from a blue line stop I believe, but the Blue Line is kinda far from, oh, anything. Still, I will make every effort to get there for some portion of it. :)