I have purchased a new game in the last few days. It is right for me because it does not require that you play it two hours a day, you can play 10 minutes or an hour and you will still make progress.
I bought its first incarnation about one year ago and now here I am with the second version. If you want to buy something that can entertain you and also make all those little gears in your brain to start rolling, I think that you should buy More Brain Training.
It is easy to pick up, but very entertaining. It is fun. You can play it with friends, brothers, sisters, wives and so on. I think the competition between two or more individuals makes the game much more fun (my girlfriend and I play it every day, of course!).
Last but not least, you get to remember how to count using your mind and not the calculator.
Andrea Trasatti's tech notes and more 