This is the book I used to learn measure theory. There is now a second edition featuring a slightly more friendly format, and a whole new chapter on probability.
I don't remember any lacking proofs with one exception - the approximation-by-simple-functions proposition. I guess this is because Cohn somewhat delays the introduction of the general definition of measurability. Rudin gives a concise (and unusually clear) proof in Real and Complex Analysis, Thm 1.17.