Robopon: Sun Version, Robot Ponkottsu Comic Bom Bom Special Version, Moon Version, and Star Version (Hudson and Red Entertainment, 1998, 1999)
A series of Pokemon-likes involving customizable robots, of which only Sun Version ever released in the US. They all used the IR sensor to handle trades and give in-game bonuses for detecting other sources of infrared, which unfortunately makes it rather expected that this green screen is all I can show.
Robot Wars: Metal Mayhem (Tiertex/BBC Multimedia, 2000)
Tiertex games have a way of crashing before getting to gameplay, and this is no exception. It appears to have been a licensed spinoff of a robot fighting TV show.
Rocket Power: Gettin' Air (Tiertex/THQ, 2001)
This Tiertex game reaches the "Press Start" screen, but pressing start doesn't do anything. At least there's some decent music to listen to while you stare at this logo.
Rockey Mountain Trophy Hunter (Xantera/WizardWorks, 2000)
A hunting game where you move a cursor around a top-down map and press select to switch into a first person shooting mode. The wind seemed to be pushing my bullets in exactly the opposite direction of the wind arrow, and I also never needed to reload.
Rokumon Tengai Mon-Colle-Knight GB (Kadokawa, 2000)
A Pokemon-ish game that's also a manga spinoff. You need to move around this grid until the little bird in the top right starts making noises to indicate you're close to a monster, and then you'll capture it if you can move on to its square. There's a lot of talking involved, and the one battle I saw was just swapping basic attacks until I won.
Roland Garros French Open (Visual Impact/Cryo Interactive, 2000)
A tennis game that has a real person's name in the title, but that uses all fake players. I picked the first character in the list ("Heidi") and then proceeded to get blasted in the first game because there doesn't seem to be a way to hit the ball with any real force, so the AI never has much trouble getting to it. Which is just as well, because the music is terrible.
Ronaldo V-Soccer (Bit Managers/Infogrames, 2001)
For some reason you run at approximately the speed of a 90 year old man with a walker when you have the ball, which means passing constantly is really the only way to get anything done. Unfortunately, the passing controls aren't very accurate. I can't say it's the worst soccer game on GBC because there've been some nearly unplayable ones, but I definitely wouldn't recommend it.
Roswell Conspiracies: Aliens, Myths & Legends (Crawfish Interactive/Red Storm Entertainment, 2001)
Naturally, this game with two alien references in the first three words of the title opens with you hunting werewolves in London. It's a really clunky top-down shooter with horrible music and indistinct graphics. If that sounds harsh, it's because this game sucks.
Rox (Altron/Titus, 1999)
Tetris with dominoes, but also the gems from Super Puzzle Fighter. I have absolutely no idea what causes blocks to disappear, but I was able to clear the first level through sheer luck resulting in some large matches.
RPG Tsukuru (Kuusou Kagaku/ASCII Entertainment, 2000)
RPG Maker for the GBC. It lets you start playing your game before you've made it, which results in staring at this map with no character to move. There are a bunch of blank menus you can access, but no way to quit the game without turning off your system. It's RPG protagonist purgatory.
Golf Ou: The King of Golf
John Romero's Daikatana
Kakurenbou Battle Monster Tactics
Keitai Denju Telefang
The Legend of Zelda: Link's Awakening DX
The Legend of Zelda: Oracle of Ages
The Legend of Zelda: Oracle of Seasons
LEGO Island 2: The Brickster's Revenge
Metal Gear Solid
Millennium Winter Sports
Pokemon Crystal Version
Pokemon Card GB2 - GR Dan Sanjou!
Pokemon Puzzle Challenge
Pokemon Trading Card Game
Quest for Camelot
Return of the Ninja