When I haven't glanced at Ricardo for a while I have this image of him in my head as being dull. He fretted a lot about value, then he wrote about the returns to the factors of production, he had a sliver of solid Econ 101 in his trade chapter, and then a bunch of stuff on taxes.
The machinery chapter alone was fairly interesting.
That's the image I always have of what it is to read Ricardo. But every time I pick him up and actually read him I'm surprised at how good a read it is. For one thing he writes clearly and basically gets to the point. Adam Smith goes on and on about the same point (at least he's a good writer - but it's hard to push through much with how much he writes). But there are actually very interesting ideas. The rent chapters especially always surprise me in how insightful they are.
As a side not, Agnar Sandmo's (half!) chapter on Ricardo (he shares a chapter with Malthus - they believe it or not - they don't even get their own!) is really excellent. He covers all of Ricardo's ideas of course but in just two pages or so of that treatment he distills the point down so well that I almost don't want to assign it so I can just use it as lecture notes. I won't - I'm going to be using Sandmo. But the Ricardo section especially is just that good.