Played through 3 more stages, and it seems Stage 3 is where Treasure decided to reveal that they can be cheap S.O.B.s because the difficulty definitely spikes severely toward the end of that stage. I loved Stage 4 visually and it has a great sense of movement, but the bosses in that stage are incredibly cheap (particularly the final one, which has an attack that is nearly impossible to dodge and she does it continuously until you die or you manage to take her out with a lucky shot). Frequently, the game will just toss boss after boss at you, sometimes without the benefit of a health pickup. Strangely, Stage 5 was incredibly easy and quite fun as you race through a stage on a motorcycle in a sequence that reminded me a bit of F-Zero or the racing sequence in Chrono Trigger. As I get further into the game, I really appreciate how Treasure continuously changes up the gameplay to keep things interesting. One moment, you may be running or flying through an area on the Z-axis, another you might be moving left-to-right like an old 2D shoot-'em-up, and another you might be moving upward trying to carve a path while simultaneously killing other enemies and avoiding a boss. Often, the game will string these together in one sequence, which is pretty exhilarating. I just wish the game didn't require such sadistically exact timing from the player in some of these boss fights. You really have to time your dodges well.
I'm also surprised how somewhat easy-to-follow the story has been, especially considering how much its convolution has been brought up on various podcasts. Aside from the horrendous dialogue sequence about "what is a human?", the writing and voice acting hasn't been too horrible, either.