The controls are super simple - just slide the boxes around the screen with a swipe motion. You pick up a number 4 box and slide it into another number 4 box. That will then become a number 5 box and you continue matching as fast as you can.
There is a timer and when it runs out, a new row of boxes will appear at the bottom. When you get to 10, you will see some of the boxes becoming linked in pairs. This makes it harder to slide them around but you can break the links by matching one of the linked boxes. When you get to fifteen, boxes are linked in threes and if you do get to twenty, boxes are linked in fours.
The aim of the game is to get to twenty but that isn't the end of the game. You keep going to see how many twenties you can make. My high score is 6 but I have no idea if that is good or not. (Update: My high score is now 12!)
I love this game and played it for hours on my plane trip home last week. I'd give Twenty a 10 out of 10. It's simple to learn but hard to beat. I'm so hooked on this game, I've even paid out a few dollars for the upgrade! That just gives a few extra twists to the basic game and isn't necessary at all.
There are no adverts and the music is actually quite soothing.
If you have a game you'd like to suggest, you can contact me on Twitter @NevAHAddict or leave a comment below.
So until next time, have fun!