I will try to keep this as short as possible <img src="smileys/smiley1.gif" border="0" align="middle" />
Construct 2 is the first software I bought in a long time (and I don't usually buy software).
First of all, most of us are hobbyists and in best case Indie. What we need ? We need easy software (less coding) and tools as cheap as we can get. Quick comparison of 3 engines that I tested before:
In the performance order (the things you can do with the engine):
Unity3D > GameMaker:Studio > Construct 2
Features/price ratio:
Unity3D > Construct 2 > GameMaker:Studio
Construct 2 for nice 2D games done fast, available in browser and almost on all platforms. A disadvantage that I see is that exports only HTML5 and in order to port your game on other platforms, you will need 3rd party tools.
Unity3D for better quality games but you need coding skills (C#, Javascript or Boo) and more time to spend. Also for Indies is free until they reach 100.000$ if they put Unity3D logo at the start of their game.
But if you want to make a decent commercial game you will need at least one good programmer and one graphical artist (it's very hard for only one person to make a good game).
GameMaker:Studio if you want to spend more money, learn a proprietary programming language and have headache using the Layout editor. With Unity3D bringing default support for 2D there will be dark days for GameMaker:Studio.