Ohasuta Dance Dance Revolution GB (Now Production/Konami, 2001)
DDR is back after many dozens of games since the last one appeared, but it's also back to incomprehensible control schemes. Right on the dpad is left, down is down, B is right, and A is up. I assume this was to deal with the dpad not being able to input R/L or U/D at the same time, but it's no more usable now than it was when this came up back in the first block of DDR games.
Ohasuta Yama-Chan & Raymond (Epoch, 1999)
A ladder action game with surprisingly good music. The main distinguishing feature is that you can press B to kick an adjacent block and remove it from the game, which lets you reach places that were otherwise blocked off and also create softlock positions.
Oide Rascal (Agatsuma Entertainment/Tamasoft, 2001)
A Tamagotchi-style game starring Rascal the Raccoon. You have a surprisingly large number of ways to interact with Rascal, who is also capable of talking, and there seems to be a light story going on as well. The music is absolutely horrible, but on balance it was probably a good pick for fans of the genre.
Ojarumaru: Mitsunegai Jinja no Ennichi de Ojaru! (MTO, 2000)
A collection of very basic shrine festival-themed minigames. All of them have background music that sounds bizarrely like "Deck the Halls."
Ojarumaru: Tsukiyo ga Ike no Takaramono (Success, 2000)
A roll-and-move game that spent all its memory on fancy animated scenes and thus has to look like this for the actual game. It's no more interesting than any other roll-and-move.
O'Leary Manager 2000 (Live Media/Ubisoft, 2000)
Another soccer manager game, except this one also lets you be a player/manager and just play regular arcade soccer. It's probably for the best that it's mostly a management game, though, because it doesn't give you any indication who you're controlling on defense and there aren't many animations for much of anything, so playing it is mostly just alternating running down the field and scoring every few seconds.
Othello Millennium (Tomcat System/Tsukuda Original, 1999)
It really is just Othello, but with the added bonus of an AI that takes an absolutely unacceptable amount of time to move. It seems to get slower every turn, and by turn 5 it was already taking upwards of 10 seconds. Why even bother playing against a computer if it's going to be that slow and still not very good?
Ottifanten: Kommando Stoertebeker (Kristelkratz/JoWooD Entertainment, 2001)
German auto-runner starring whatever this monstrosity is supposed to be.