I had also hesitated to mention Captain Forever : Theorically it allows you to build spaceships in very creative ways. But given that you are very dependant on the pieces you manage to collect and your skill at preventing them to get blown back away, I couldn't really explore this aspect very far.

But I'm being (very indirectly) reminded of it by <span class="bold">Space Run</span>, which I expected to be a bit more build-your-own-lego-spaceship and less set-your-defenses-with-new-towers-on-each-blank-map than this review unfortunately seems to say.