Got and read book #5 as well as the Michelangelo stand-alone.
Number 5 was good and reveals some more about the turtles' backstory as well as some more clues about what is happening here along the lines of what was speculated on up-thread.
The book ends with Michelangelo, Donatello and Leonardo getting their separately colored bandannas (making the whole identification issue I had easier) and Raphael getting his sais.
The Michelangelo one-shot/stand-alone..... Eh.
The story in it was decent, Michelangelo is out alone on New Year's Eve and he wants to be a "party dude" and enjoy the night rather than being at home with his brothers doing more boring stuff. It's a good story but the art in this book is atrocious and inconsistent. Michelangelo's size changes constantly, the coloring is poor and it's just really a very, very, ugly book. It looks like it was drawn by a grade-schooler. They should have had Eastman draw this, the guy who does the regular books or even the guy who did the Raphael stand-alone last month. It's an okay book, one to have if you're collecting the trutles' stand-alone books. But the art is just horrible.