Was looking to see if anyone here had interesting insight on some games that saw drastic changes when the were localized from Japan to North America. Obviously Yume Kojo: Doki Doki Paniku would be one of the most extreme examples, but I'm interested to know what other games might have very noticeable changes from their Japanese versions to their North American versions.

What about the Nintendo Famicom Disk Player. If i'm not mistaken that added a second sound channel(?) I'm not a really technical person and don't notice something like that very much, but I feel like Simon's Quest has a superior soundtrack on the disk system? Are there any other examples like that?

If I'm also not mistaken the Nintendo Famicom had a microphone on the controller? One of the bosses in the original Legend of Zelda could only be beaten if you blew into the microphone? Are there any other examples like that where different hardware designs forced changes like that during the localization?

It's Pols Voice that yelling into the microphone works against. For the North American version they changed it to arrows.

The Famicom four player adapter works differently than the NES FourScore, so a couple of games like Super Dodgeball and Stinger lack the ability to do more than two players on the NES versions.

I dunno if they're massive but the only ones I can think of are Power Blade 1 and 2, Tecmo Cup Soccer and Maniac Mansion (graphics only).

We all know about Mario 2 & Doki Doki Panic. But here are two others.

Extreme Example 1: "Yo! Noid" which uses "Kamen no Ninja Hanamaru" as its base for conversion. I haven't played Kamen no Ninja Hanamaru completely through. However, it seems all platforms, enemies, etc. are all in the exact same spot as Yo! Noid's. The game itself is completely converted graphically despite it being functionally the same.

Extreme Example 2: Power Blade & Power Blazer.
I'm not sure how these are the same game. People consider them the same somehow because they use the same code base/engine and a few elements are left unchanged? Maps are completely different and the game looks and feels nothing the same.

Enable Kamen No Ninja Hanamaru Intro
GAUGILAE
I made a code to re enable the intro with the bird but he's glitched in yo noid

Famicom Kickle Cubicle allows you to play the boards in any order, whereas the NES version you're on a set course.

Some Famicom games use expanded audio compared to other localizations. Castlevania III and Gimmick! come to mind.

Famicom Millipede has a nicer presentation over the NES version.

Some had different difficulty. Bayou Billy and Ninja Gaiden III are more difficult on the NES, SMB 3 is slightly more difficult on the Famicom (a hit puts you back to small Mario regardless of suit.)

The Famicom Lolo games have completely different levels than the NES versions.

Monster Party.

Dragon Power was a Dragon Ball game
Whomp 'Em was also based on another manga IP which eludes me now

Same with Chubby Cherub.

Maniac Mansion was one of the first ones to come into my mind... One of my favorite NES games.

Graphics, music and sounds are completely different between the two.

I prefer the NES version by far.

Yep 

I think the Japanese Contra had a little story added on that was removed in the US versions, and maybe other things that I can't recall atm.

And of course, "Probotector".

It was originally a PC game though. It's quite collectible for PC collectors; its the game that made a name for Lucasfilm Games.