I’d have to actually read the books themselves to have a proper opinion on his handling of Wonder Woman and the DC Multiverse.
My experience reading Morrison’s work is that he’s very hit and miss with me. When it comes to his handling of women, he can either write some truly amazing stuff (he did write a great Catwoman in his first volume of Batman Inc) or resort to some truly atrocious characterisation as a way of moving his story forward like he did with Talia Al Ghul throughout his Batman run.
With Wonder Woman, the main concern that I have with his writing her is his strong emphasis on sex, which in itself is not a bad thing, but Wonder Woman should not be reduced to her body or sexuality. It spectacularly misses the point of her being an icon of female liberation and that her character exists precisely to challenge many preconceived notions that are taught to us about gender throughout our lives. That is the strength of her character and any straying from that concept weakens her power (something we’ve already seen happen across two universes in the mainstream comics).
Originally the Wonder Woman: Earth One book was supposed to go to Greg Rucka (who in my opinion has a better handle on her character and female characters in general), and it saddens me greatly that he was robbed of that opportunity to hand the project over to a writer who’s vision for Diana is dubious at best. If Rucka had remained on the project, I would buy this book in a heartbeat.
Lastly, Morrison’s handling of the Multiverse could similarly go either way. It can either be truly amazing or absolutely atrocious. My only lament is that we didn’t get the Geoff Johns-written Earth-2 that we were originally supposed to get for this series since he had a very good handle on this world post-Crisis. I loved that he stayed true to the original concept of Earth-2 and I was hoping to see more stories with Helena Wayne and Power Girl written by him.