In my experience, running games are either hit or miss. Ninja Rush for Android, though, happens to hit the nail on the head.
The Android marketplace is filled with running games, and most of them are not very good. They have poorly animated stick-figure drawings for characters, and overly repetitive backgrounds that will bore you within seconds. That's why Ninja Rush is a breath of fresh air. For such a simple concept, and one that's been seen over and over again, it's got a lot going on.
For starters, the game is very well made. It's not quite 3D caliber, and the colors aren't especially vibrant, but there's something about this particular art style that's very cute and fun.
The controls aren't limited to running and jumping, either. Sure, a single tap will make you jump, two taps will make you leap higher, but it gets a bit more advanced than that. A quick swipe to the right or left will increase or decrease your speed, and a ninja star button fires stars at your enemies.
There's never any confusion on how things work. Ninja Rush has a brief "training" tutorial at the beginning of the game (you can skip it if you want), which helps teach you how to play.
The game's setting also keeps things interesting because it's not just leaping over rocks and gaps in the ground. There are enemies that must be killed, and sometimes, you have to use your ninja skills to swing to the other side of the cliff. There are also power-ups that help you regain your health and pick up speed.
The game's replay value can be attributed to its achievements, though. There are 20 or so different "awards" that recognize when you complete difficult tasks. Some of them include Fantastic Jumper, Runner Master, Eliminator Elite or Super Ninja, which is the award for earning all of the game's achievements.
This is a very fun, simple game that's surprisingly addictive. It's free, and you should definitely check it out.