Students have mixed opinions about the classes at RPI. Most agree that the professors are, as a whole, very smart. However, their ability to communicate that knowledge to students is variable. Some are excellent in relating to students, while others can barely speak fluent English. Another claim against professors is that they are too concerned with researching and getting published to put the time and effort into doing a good job teaching.
Your best bet is to talk to an upperclassman who has taken classes with professors before, and find out who is good and who to avoid. A student's interest in the subject also plays a huge role in deciding how much he or she will enjoy and take from a class. Pick a major that you're going to enjoy, but also pick one that you've got a good feeling about-again, talk to other students in the programs, because your major will make a huge difference. RPI is a demanding school, and students here are expected to do a lot of work, both inside and outside the classroom. If you are not truly avid about your field of study, you may find it hard to keep yourself motivated to get all your work done.