I had the opportunity to watch this recently and it didn't hold my attention. It felt very different from traditional comic book movies and at first I didn't even realize what I was watching. About halfway through I just gave up trying to watch it. Not surprised this one bombed.
There's definitely a big shift in tone that takes it from a bit of a thriller to straight up blockbuster fest right at about the half way point. Personally, I feel like the first half is a lot tighter for the most part, but still a bit of a snore fest. I think part of the "slog" is the added bits to flesh out more of the Clark side of the story. They should've really taken out the knightmare and time travel bits or only left one of them in the cut.