I'm somewhat with both of you. The pace definitely felt like it picked up later on, but at least some of that was due to the lack of a long and drawn-out section just prior to the Elite 4. I've generally hated Victory Road, so its removal was very welcome to me. I do agree, though, that this means that the game does feel rushed, especially when it comes to Spikemuth.
Post-game is a lot better than ever before, and this means that I've managed to reach level 100 with more than one of my mons for the first time! Raids aren't dull yet, and that new G-max forms keep on reaching us keeps things fresh. I'm still on the look-out for Duralodon, Lapras, Gengar, Machamp, and any others that I might not even be aware of.
Overall, I feel it's the best Pokémon game ever, and it will become even better with the expansions. But I also can see why some may be disappointed along the way, because the focus changes halfway through from standard Pokémon fare to a much more battle-focused experience. Wether this is due to time constraints, or a deliberate direction is unknown, but it definitely has led to some thinking less of the whole game because of it, and the announcement of expansions will certainly exacerbate that feeling in some.