In general, Grinnell academics are very strong. Like all schools, some classes/professors are hit or miss, but the majority of our professors are great. I can't be certain about this, but I'm pretty sure each of my professors has known my name -- at least, I can't remember any who haven't. I've spent time with several professors outside of class, and most of them have been kind, helpful, and interesting. It's nice to have professors treat you as an equal.
Students study pretty much everyday, though I tend to spend time with the more academically inclined, so I might be misrepresenting a slice of the Grinnell population. Most students I know, at least by the time they reach their junior and senior years, think we're assigned too much work -- it can get pretty ridiculous, and triaging often becomes necessary if you want to sleep at all.
Class participation is very common, and most professors expect it of all their students. I'm a fan of this system.
As regards student competitiveness, this is one area that I think makes Grinnell pretty unique -- we're not very competitive (with each other). My education at Grinnell has been uniformly characterized by cooperation and assistance among my classmates and other students. When we're competitive, it's with ourselves. We're really driven, and often expect too much of ourselves. That's part of what makes Grinnell academics stressful.
A Grinnell education isn't really geared towards getting a job -- we are, after all, a liberal arts college -- and learning for its own sake is definitely a part of our culture. I've had intellectual conversations outside of class with almost every student I know, and they're often very interesting, informative discussions. They're entertaining too -- Grinnellians are good at merging the intellectual with the ridiculous/humorous.