Grant Morrison doing some more work with the JLA. How can that ever be a bad thing? That's exactly what I thought until reading this arc. I think I might have appreciated this story more if I knew anything about the Ultra-Marines, but I didn't. I also didn't really know anything about the mini universe that the JLA are trapped in for the first issue. Combine this with only a casual knowledge of the JLA and you get a story arc that, while well written, wasn't all that enjoyable for me.
Morrison is a writer who I have the utmost respect for and after just finishing We3, I was looking forward to reading this. I wanted to read a story about the JLA written by Morrison, not a story about the Ultra-Marines with the JLA playing only a partial role in the overall plot. The entire first issue is primarily devoted to watching the Ultra-Marines take on Gorilla Grodd and Batman working with one of the Ultr-Marines on a way to contact the rest of the JLA in the mini universe they were trapped in.
The middle issue sees the plot advancing and being used simply to set up the big throwdown battle between the brainwashed Ultra-Marines and the JLA. I don't have anything against big superhero battles and the many different match-ups were written well, but since I didn't know anything about the Ultra-Marines other than they were being mind controlled, I didn't feel invested into the outcome of the battles. I just didn't care. In the end, Grodd is stopped and everything is wrapped up nicely, and I'm left feeling a little empty.
The art by Ed McGuinness, although very cartoony, works nicely. I really didn't like his style when he was on Superman/Batman, but it seemed much better suited to this title. At times, though, I wished his style was more consistent. When drawing Grodd and his gorilla compatriots, Ed would use a more detailed, less cartoony style than when he was drawing the JLA and Ultra-Marines. Personally I wish he would have used this style the entire series through, but as it is, his work functioned just fine for the story on hand.