Qwirkle is another of those "simple yet complex" games. All you get in the box are 108 wooden squares, a bag to hold them in and the instructions. You play with 2-4 players (more players is better) and then you have to start placing the tiles down to try and gain points which are toted up at the end. Each square is one of six shapes in one of six colours (there are 3 of each tile) and the main aim it to try and make lines that have either the same shape in each colour, or the same colour with one of each shape. Each player has 6 squares and you take it in turns to play. It sounds both uninteresting and boring, BUT it is a very tactical game - you end up making a huge crossword puzzle type shape and as the game goes on more possibilities appear. I've played it with adults, kids (from 7 upwards) and everyone has enjoyed it. The game can take quite a long time to play (the last game with 3 people took 50 minutes to complete) but it is enjoyable and you need to concentate on the board between rounds to see if you can get your pieces in.
My family (and extended family) enjoy it.