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.

I really liked Polycode.

I hope you're not recommending anyone use Construct Classic though. It filled a market gap for its time but some users reported it crashing constantly, a problem that seems to have been fixed well in Construct 2.

I did my own personal tests of Game Maker Studio vs. Construct 2 and Game Maker was 15-35% faster in a "many objects with physics" test. However, this was before that new compiler for Game Maker came out.

Honestly, I can't recommend for or against, as I just tinkered a bit with it to see if I'd like it. This is the first I've heard of a lack of stability though, but if you say it, I'll believe it, since like I said, I really didn't use it but enough to figure out that I didn't like the "coding" section of it. I DID like the behaviors etc... that made gametypes automatic.

So GMStudio was faster before the compiler came out? That's a good thing then, considering I use GMStudio :) Honestly though, I don't think that the compiler would help much in that exact type of test. I say this because the internal GMStudio's game engine itself is already compiled to the native platform, while the GML scripts are technically still interpreted. The interpreter itself is faster than before GMStudio because the rewrote it with C++ and made some optimizations, whereas before it was done in delphi, and even included a compiler with it, making things possibly slower, and for sure more bulky. But, the new compiler that came out recently will make a big difference in games that have heavy scripting, but it won't make much difference in games that have very little actual scripting. For example, if you are generating levels with scripting, or you were using my vertex skinning code to make animated models(like Quake 2 with MD2 models), that gets much faster. On Android, I couldn't even get 2 models of 1000 or so verts to run 60FPS, and even on PC it could barely do it, with the original GMStudio runner, but with the new compiler, it is suddenly full speed, and I was able to get 10 models without dropping framerate before I quit testing, though it may have been able to do plenty more. But yes, results will highly vary with the compiler.