I like some things about Construct. It has plugins etc... for behaviors and things, making certain game types easier. For example, there is a platformer behavior which includes jumping, double jumping, and I'm not sure what else besides tile collision. There is also one for Top Down Shooter, and several others that can make things easier. Gamemaker doesn't include this kind of thing, though it is more than capable of doing them, you have to find one already done, a tutorial, or code it yourself.
Speaking of coding, I could never get into Construct's D&D coding. I know that it is much more powerful and capable than GM's D&D, but GML scripting seems more powerful and easier than Construct's D&D. And I for one coming from more of a coding background find GML scripting that much easier. On the other hand, someone with a different background may find Construct's D&D easier than GML scripting.
As far as capabilities, I've understood that Construct is supposed to be pretty much as capable as GM for 2d games. The original version(now free, called Construct Classic) was pretty capable for windows games. But Construct 2 is focused on Javascript. I think this can become a problem. Javascript isn't as fast as native code, and I'm sure that it is worse on mobile platforms than on PC. On the other hand, the other things that are running Javascript on iOS and Android I'm sure are faster than HTML5 games on Mobile browsers, but I doubt that it is as good as native. This is where GameMaker shines, because it exports to native code instead. This doesn't apply to HTML5, Windows 8 Metro App, Tizen, etc... but Android, iOS, windows, Ubuntu, Mac, are all native.