Mahabobodhi Complex is very interesting. You can feel the anciant atmosphere and the "faithful buddhist scenario". Is it possible to see old stupas, little and big Buddha statues, tibetan devots, monks, tourists, prayers, poor people, children and dogs (!)living in peace inside complex.
The train travel between Varanasi and Gaya is, too, absolutly interesting. Trains are old, ugly, dirty...sensational!