Tetris

http://img22.imageshack.us/i/tetrisfront.jpg/
(a very similar concept as above)

Gameplay
Pretty simple, stuff falls from the sky, and you have to compete to complete the objective. Pretty much everything that is movable in reach is set-up to fall on you, Scorpions, camping stools, Warthogs, Revenants, you name it, it falls. One big thing to note is that there are two ways to play Tetris, you can play King of the Hill, or you can play Oddball. I'll get into the gametypes later, but for now, I'll show some general screenshots.

http://img694.imageshack.us/i/reach15593376medium.jpg/
(a straight up view of the tube (It goes past the soft barrier))

http://img824.imageshack.us/i/reach15591116medium.jpg/
(right above hemmorage looking towards the Island (the tower is built in-between the Island and the Quarry))

Theme A (KOTH)

Gameplay
Infinite jetpacks, Infinite Concussion Rifle ammo, and hills that move throughout the tower. Try to push your opponents out of the hill and score points to gain the lead. There's really not too much to explain... but I'm sure a video will help!

YouTube - Halo: Reach Tetris

Pictures, for those who didn't watch the video

http://img141.imageshack.us/i/reach15586986medium.jpg/

http://img541.imageshack.us/i/reach15587139medium.jpg/

Theme B (Oddball)

Oddball is more similar to the original Tetris than the KOTH variant is, because Oddball is about climbing to the top of the tower to grab the oddball! With that in mind, the pictures will do better at explaining the game than I will. But sadly, there is no video, well... I made a video, but it didn't give you the same feeling watching it, that you got playing it, so I just deleted it.

http://img713.imageshack.us/i/reach15588689medium.jpg/

http://img146.imageshack.us/i/reach15589795medium.jpg/

There you go
Well, I really thought I would put more into this post... but well, its a minigame, and any good minigame, needs no explaining! so Download! and have fun!

Tetris Map

Theme A (KOTH)
(If you're only going to download one, Theme A is better)

Theme B (Oddball)