This sketch was my first attempt at an Arduino project.
It's rough but functional for anyone interested in replicating the project.

Also included in the project:
A fritzing project file - http://fritzing.org
A breadboard diagram
A circut diagram
Note: The pin number may be incorrect for the LED outputs, they should be relativly easy to figure out using the init light sequence.

The game itself is a memory/reflex game based on N-Back style tests : http://en.wikipedia.org/wiki/N-back

---Gameplay---

Init Phase:
Initially a small light pattern is displayed on the 6 score lights to indicate the game has initialized.
Player one pressese the button and the center light will flash green indicating the start of the setup phase.

Setup Phase:
Player one indicates which n-back level the game should be played with by pressing their button that number of times.
The center light will flash blue once per button press (wait for the light to go out before subsequent presses).
The n-back level is also shown in binary on the leftmost 3 score lights.
Once the proper level is selected Player two can press their button ending the setup phase.

Accept Phase:
Player one and Player two should press their buttons indicating they are ready for the game to start.
Once both players have accepted the center light will flash green 3 times and then turn off indicating the start of play.

Play Phase:
The play phase is where the fun(?) happens. The center light will turn one of three colors (Red, Blue, or Green) and remain on for a short period of time before turning off for a brief period then turning on again with a different (or possibly the same) colour. The players must decide if the colour shown is the same colour that was shown x previous where x is the n-back level selected in the setup phase. For example if the n-back level selected was 3 and the colours shown were [Blue] [Green] [Red] [Blue] then the player would consider this last [Blue] a "hit" and try and be the first to push their button. This would be considered a hit because 3 previous to the current colour was the same colour. If the series had instead been [Blue] [Red] [Blue] [Green] then it would be a miss because the current colour [Green] was not the same as the one 3 previous [Blue]. Essentially the players need to remember if the colour they saw "n-back level ago" is the same one that is currently shown, if so it's considered a "hit" otherwise it's a "miss". If a player is the first to press their button for a hit they get a point and the score indicator will move closer to their side. If a player presses their button for a miss then they lose a point and the score indicator will move closer to their opponent.

Scoring:
Scoring is done in a tug-of-war style. 
At the start of play none of the score lights are on, this indicates that the score is even.
If a player is the first to press their button for a hit the score indicator will move closer to thier side.
If a player presses their button for a miss the score indicator will move closer to their opponents side.
If a player who has the score light closest to them already lit up gains an additional point they win.

Game Over:
Once a player has won the center light will flash multiple colours and the winning player's score indicators will light up.
The game will reset to its init phase after a few seconds.

---Pattern Examples (-X indicates a hit)---
nback level 2: 
[Blue] [Red] [Red] [Green] [Blue] [Green-X] [Green] [Green-X] [Red] [Blue] [Red-X] [Blue-X] [Blue]

nback level 3: 
[Blue] [Red] [Red] [Green] [Blue] [Green] [Green-X] [Green] [Red] [Blue] [Red] [Blue] [Blue-X]

nback level 4: 
[Blue] [Red] [Red] [Green] [Blue-X] [Green] [Green] [Green-X] [Red] [Blue] [Red] [Blue] [Blue]