I agree with your review for the most part, Nick. I generally enjoy Millar's work, whether is is the Ultimates or stuff like Superman: Red Son. He has a knack for deconstructing what makes a superhero popular, turning it on its head, and giving it a fresh spin. In Old Man Logan he takes a broken Wolverine who refuses to use his claws, sends him on one last mission and turns it into something enjoyable, yet also a bit predictable.
We all kind of know he's going to use those adamantium claws at some point and while the post-apocalyptic vision of the Marvel Universe is highly amusing (Red Skull as president, Hillbilly Hulk Family as low-rent gangsters...), you can kind of see where it is all going before you get there. The ending is pretty over-the-top with the whole Hulk versus Wolverine thing, it was almost like he thought he had to one-up the Ultimate Hulk vs. Ultimate Wolverine thing from a few years earlier. I did enjoy the Red Skull's trophy room and Niven's art sure was nice to look at.
I'd give it 7 out of 10, but haven't read it in trade paperback and am only going on memories of reading the individual issues.