The problem with the future stuff is it's all filler. We know that none of the stuff happening is going to matter, because it's all going to change. There are no stakes. The only way they could have made the future parts better is by making the detective work actually interesting, which can be a really tricky thing to pull off. The way the future is set up makes it really difficult to create a cast we care about as well, and when you contrast to a cast in the past that create a pretty massive emotional attachment, that creates a bit of a whiplash effect.
Gintama has been hitting it out the park for months now. It will be pretty hard to top as my AOTY.
Shogun Assassination arc had the same problem for me that most of the post-Devas dramatic arcs have. It feels like such a straight manga adaptation that it has no room to build. The fights all feel insubstantial and short, even if they should work from an exciting plot perspective. I dug it, but didn't think it was worth the huge amount of hype it got building up with the early trailer tease and everything. Ending hit incredibly hard emotional for me, so at least there was that.
Goodbye Shinsengumi seems much stronger so far, but I expect the action to run into the same pitfalls.