Rocket Mania / Bowman
As I will be spending the next few evenings in the company of a untrained and petulant "other" computer, normal service on VSX may not resume for a few days.
As a gift to regular readers in the meantime, I offer you - ROCKET MANIA! One of the most addictive web games I have ever played. Adding a Puyo-Puyo/Tetris spin to an already solid core concept of gridsquare-rotating firework fuse-connection (complete with rewardingly explosive payoff) was a touch of genius. Scarily compulsive.
If you'd prefer something a lot more slow and considered, you could do worse than Bowman (link spotted at Keelhauling), one of those archery duel games which is all about angle and speed of projectile. I'm utterly rubbish at it, though it could well float your boat...
If you can't cope with the mental strain of physics calculations, you'll find Gold Miner much more to your liking (link from from NGUK). Simple but fun.