I tried Kodu Game Lab and whilst it's not perfect, it's pretty nice.
As far as I can tell, you can't add custom 3D models.
And there seems to be a bug: when I try to assign certain programming
commands, they just don't work but the majority of the programming commands I've tried
The programming is visual which is nice and easy to use
....so less of the technical coding (well probably none on your part)
leaving more room for brain power for the creative aspect! Because I hate coding.
And I'm relatively creative. http://www.kodugamelab.com/
My first game, which I made quite lazily: (Especially considering lack of time
and while I was impressed with the simplicity, I wasn't impressed with the bugs.
E.g. the down arrow key / or S key doesn't work the way I want it....
Instead of braking, the character keeps going, forward even.
And it's got an XBox feel to it; I think
you can make PC and XBox games with it.
So while it isn't the perfect game builder, it's a nice start and probably
worth a try, especially if you want to mess around making a test game.
"Sometimes you gotta run before you can walk." - Tony Stark, Iron Man.