Issue 4 was good.
I'm still not liking the art too much in these books. It's okay but I would've liked to see something more dynamic, interesting and "realistic looking." The art in these books is somewhat angular, blocky and lines look hairy as if they're from a rough draft or something. Coloring isn't great either. But whatever, the book has still be good.
I guess they're doing a mini-series of one-shots, one book for each turtle over the course of the next four months. Pre-release stuff claimed the Raphael book was coming out in November (yesterday) but has been delayed to next week. The second book (December's book, but not sure if it's being pushed back to January) will center around Michelangelo. From the preview of the Raphael cover the book looks to have bit better art to it. More like I would hope to see.