I just read the 8-issue Didio-Giffen OMAC series in a trade.

There were a few fun moments, and Giffen's art is very consistent with the definitive Kirby material. But Didio in the writing department dropped the ball.
I liked the Spawn of Frankenstein's part in the story, and on one level it was a fun parade of monsters. But it was just a steady stream of walk-on characters, with no development or depth.
Most annoying for me was Tuftan in the last story, where by all appearances we are teased to think Tuftan and Ceasar are the characters from KAMANDI, seen here in an earlier adventure, but are just similar characters who happen to have the same names. And it ultimately goes nowhere.
The Brother Eye narration mixing "Eye/I" is really annoying too. Giffen did his part to make it a good series, too bad Didio couldn't hold up his end of the deal.