I think DE's is a little harder than Calc II, actually. You need to be very up on your integration and algebra, as Rido said. DE's is integration on steroids. The difficulty with DE's is that it doesn't come across as a course that is as unified as Calc II. In Calc II, you do one thing all semester: pick a problem apart (analyze), solve the small problem, and integrate to find the whole solution. In DE's, you have one method for one kind of DE, a completely different method for an only slightly different DE, and so it goes. The existence and uniqueness theorems are, perhaps, a unifying thread, but they do not tend to be emphasized in sophomore-level courses.
It's an extremely important course, though. It's where the rubber meets the road. You get quite a few applications in Calc I, II, and III, but DE's is by far the most applied. You can solve circuits, and mass-on-spring systems, and many other real-world problems of genuine interest (you can earn money solving these!).
