I think Marcus is a dumb*****, like quite a few of the other human villains. It seemed to me that he didn't really understand the full scale of what he was doing, like Lawrence III and Molly Hale. Although Molly was a little girl and she was far less capable of that kind of comprehension.
What he did to Arceus was unacceptable and the movie's ending would have been more satisfying if the fall ended his life. The Silver Water concept makes more sense to me now, but I wonder what materials are in it precisely, and how Marcus got the idea for it.
My thoughts on the parts I watched;
The fight scenes were awesome, as usual for Pokemon battles. Especially when Palkia, Giratina, Dialga, and Arceus are duking it out. However, it was a little too one-sided for the most part.
Although I wouldn't support the element being removed, Brock was kind of being annoying when he was heartbroken over Sheena's romance with Kevin. But...I know, I see it all the time when I watch Pokemon (not the BW series), even since the days of the original series.
I don't really think it was necessary for the writers to put the Team Rocket trio in this movie, since they have little to do with the overall plot of the movie, although the scenes they appeared in were sort of funny. The parts where Pichu lead Pikachu and Piplup to the dungeon keys were also humorous.
Another thing I thought was cool happened to be the powers Sheena and Damos possess, and the scene where Damos struggled to communicate with Arceus to free him from that mess was epic.
One particular part though with Jessie (towards the beginning), that look on her face was a little creepy.
And another thought on some of the scenes I watched; I also enjoyed the scene that showed Arceus returning life to Michina Town, it was a rather lovely site.
Overall, I'd say this was an enjoyable Pokemon movie, and I honestly hope that the anime's staff makes another one with this quality.