Seveneves started off strong, but then turned into a real slog. It could have been a great 200 page book, but at 600 pages I was just glad to be done with it and expect it to be the last thing of his I read. The Baroque Cycle felt similar, even though it contained many of the characters I loved from Cryptonomicon, but I just couldn't make it through it.
I see there are people here who like or love it, which is great. I am not surprised to see others here echoing my feeling that it was quite a slog to get through.
Stopping at Act 2 is probably not a bad idea, though I feel like Act 1 is a lot of setup that pays off in Act 2 so I wonder what the point would be.