Here's the ad-supported (there are interstitial full screen ads between levels) Cannon Mania in action:
A well done splash screen that gives a pretty good feel for what you'll be doing in the game...
... except that cannons are used, rather than tanks - perhaps there were defense budget cuts in the Cannon Mania world?
Ten different backdrops make up the ten different levels, with a vague pretense that you're travelling through a land. Hey, just tap through this screen, you want to start launching rockets!...
And here we go. Part old fashioned cannon, part futuristic rocket launcher, you have three 'cannons', each of whose barrels are constantly moving up and down asynchronously. Tap the screen to start a round of firing....
In each level, your opponent has the same fire power - in this case though, we've managed to hit his nearest cannon five times, which means its power bar is down to zero and flames erupt, etc.
As the levels progress, there are more cannons and more challenging terrain to fire up/down.
You also get a score at the end of each level, the game keeps track of your highest in completing in each level, should you wish to go back and try to improve it.
Although there's a certain randomness introduced by the constantly moving cannon barrels, there's also some strategy in keeping an eye on which of your cannons has the most power, knowing which of the enemy cannons you want to knock out next and timing your screen tap so as to be optimised for the shot you want - and any other rockets from the other cannons which hit a target are a bonus.
A nice diversion, though the ads are indeed quite intrusive, not least because it's far to easy to follow the ads with a misplaced keypress and have to keep quitting the browser to get back to the game - or maybe this was the developer's intention.
Cannon Mania is free in the Nokia Store here.