I've been on a similar quest and ran across a few other tools not mentioned here:
I've tried a few other weirder ones too.
Alice is a 3D game / dev environment which is open source - looks kind of clunky.
Kodu, going beyond Gamemaker on the easy/limited spectrum, aimed at kids, lets you build games with an Xbox controller. free from Microsoft Research
Scratch, from MIT Labs, is free and really basic 2D, aimed at getting kids into coding. Visually clunky. Flexible though.
Going waaaay back to Papert's LOGO, Microworlds JR lets you write in logo, allegedly. Needs an update to be useful, IMO.
For me, so far, it's coming down to Construct 2 vs Stencylworks...though I'll check out how easy it is to build a decent 2D game in Unity, as I know and like Unity.