I have actually made a few "games" with GM (sadly lost to the sands of time) and while I don´t think it´s terrible, when I tried C2 it just instantly clicked with me in a way GM never managed to. The rest is history.
I don´t think GM is terrible, just not for me.
I agree, i have used GameMaker Studio 1/2 in the past, I think construct does alot of thing better (GUI,Instance Management, Visual Programming, Engine Updates ....). and things are more intuitive, and it's super fast to add feature/prototype your game. and with the hard work Scirra is doing adding new features/ bug fixes as quick as they do... It's just a matter of time before one of the many talented people using construct make a hit game, and give the engine recognition.