This week I rediscovered the Mindstorms Storm Runner game. Lego turned off this game some time ago, and I was glad to see it back - I have spent a fair bit of time over the last couple of days playing it.
It runs in a browser - although you can only save games with Internet Explorer and a Microsoft VM setup. The idea is that you have been stranded on a distant planet, with only a bay capable of constructing large RCX based robots. You must construct them, and then program them so you can explore the planet and eventually find a way off it.
Graphically it is a 2D top down - but the real magic is that you get to use your RCX code skills with the game - which is quite fun.