Capital is pretty difficult, though if you're enthusiastic than go for it. I just thought I should include what I said to the OOP:

Personally, I think the best introductory work for someone who doesn't have the patience for The Principles of Communism (and I don't have that patience myself) is Engels' Socialism: Utopian and Scientific, here as text and here as an excellent audiobook.

It's personally my favorite audiobook (not that I listen to a ton), but that's because I think the reader's dry tone is charming and works well with the type of humor Engels occasionally employs.