Re:
The Messenger:
Just got to the start of the 16-bit part- game clock says it took three hours and 34 minutes to get there. There were 8-10 levels, with boss fights, culminating with a kind of Mega Man-esque Dr. Wiley stage where you have to go through a series of challenging rooms before facing the "final" boss of this part of the game. The 8-bit portion on its own was long enough and satisfying enough that had that been the whole game, I still would have loved it! Now it feels like I'm playing the sequel on a SNES!

Other stuff:
-You get unlimited lives. There's save points throughout the levels and you respawn there when killed.
-When you respawn, there's a penalty in the form of a little demon who will follow you around and eat the crystals you get until he's had his fill.
-You can buy an item at the shop that will reduce the amount of crystals he eats.
-Besides buying abilities, you also will be given new ones as you progress. Combine those with upgrades and you'll be able to glide/attack, use a grappling hook, swim fast, and more. It made a lot of the jumping areas a snap since there's so many ways to move around.
-Difficulty so far feels pretty fair. Some parts are pretty easy...maybe too easy, but I ended up dying like 50 times from what I've played.
-The levels are linear, but there are hidden paths/rooms you can find with extra crystals or challenge tokens. There's like 45 of these tokens and getting them requires going through a hard platforming section to get them. Not sure what getting them all does. It's completely optional.
-Saw a small amount of optional paths that I couldn't get to while playing. Am assuming that you either return to the 8-bit portions of the game with new abilities or there's a new game+ that lets you get to them?
The game is just fucking amazing. It's not like Bloodstained Curse Of The Moon since it's more akin to Ninja Gaiden than Castlevania, but if I had to compare the two, this shits all over it in everything but the difficulty department. Just way, way more fun and there's some pretty humorous banter too.