Blokus is a great game for 2 or 4 players. You have to try and occupy as much of the board as you can, using the odd shaped Tetris pieces of your colour. However, you cannot place the adjacent to your pieces or randomly far away. They have to be diagonally touching one of the corners of your piece already on the board. We like this game because of its abstract concept and strategic play.
“Blokus (officially pronounced "Block us") is an abstract strategy game with transparent, Tetris-shaped, colored pieces that players are trying to play onto the board. The only caveat to placing a piece is that it may not lie adjacent to your other pieces, but instead must be placed touching at least one corner of your pieces already on the board.”