Mike, I have the exact same situation! In fact, I'm browsing the forums as a way to procrastinate on putting together my feedback email. 
I think one key thing is to be clear on why they're asking for feedback, or what kind of feedback they're asking for. Do they really want to know what you think, or are they just looking for a rubber stamp "looks great"? And, are they planning (or even able) to do anything with your feedback? If the course is done and about to be deployed, there may be little that can be done even if they want to. On a related note, if you suggest eight things they could do better, are you going to be the one fixing those eight things? (that could be bad or good, depending on your viewpoint!)
If the course is really still in development, you could use the "This is a great start" approach - I find that often works well to protect people's egos but still give constructive feedback. "This is a great start. There might be some things you could do with the content you have to make it more engaging, maybe we could brainstorm some ideas together."