Campbell has produced a volume that is accessible in terms of content, and the price won’t bomb your book budget.
And there’s even a preview: Campbell has done a series of posts at the Zondervan blog on verbal aspect. Take some notes on these posts, memorize a few basic definitions, get familiar with his examples, and you’ll be ready to read the book, which will get you ready to answer questions and dialogue on these issues when you get asked what you think about the aspect of the verb (and you never know when that might happen!).
Here are the posts:
I highly recommend this book.