I'll be in the minority to say that I liked Chapter 3 although it's definitely filler, but there's a couple bits about the design I haven't seen mentioned anywhere:
The first time you get to the green room and talk to the NPC (don't remember if it's ramb or not) who says the game's a kind of twisted linear a-to-b version of a previous game that was much more open-world is an obvious reference to the secret route, but there's another way more subtle joke here: The entire scenario for the TV show including Tenna, his banter with offscreen producers, the flipping through different channels during the bossfight etc is a direct lift from a very cult open-world Wii game named
Little King's Story even down to the object heads both being rulers of tv-themed areas populated by lots of little black canon-fodder humanoids. The biggest difference between the two is Tenna's analogue (TV Dinnah, because LKS has a braindead translation, uses Japanese terms everywhere and come the fuck on Terebi-san is
right fucking there) is characterized as a chill newscaster rather than bombastic gameshow host. It kinda stunned me how direct the lift is. Seriously look at this fucker:
The other bit I haven't seen pointed out is Tenna's boss theme being a mashup of bits of classic NES/SNES music. Someone pointed out the Turtles in Time instruments but the opening is decently close to the
boss theme from that game, the main bridge is extremely close to
Johnny's Theme from Chrono Trigger and the droning bit is the
escape sequence from NES Metroid.
Also, Tenna having classic Hanna-Barbera facial features was a nice touch. I want to say his antennae are directly from something as well but I can't place them.