I also chose Gamestudi because the programming language is very easy to learn, has power to make all kinds of software in no time compared to other languages, it`s cheap, stable, has nice graphics althogh Unity and Torque are better here, it has a big, helpful, critizising and friendly community and nice gamemaking tools (WED,SED,GED,MED). You can customize the fast rendering engine by writing plugins in C++ and publish the game without any license payments. And, there`re many community add-ons like IntenseX, Intense Pathfinding, Anet or IceX that make game design and programming much easier. Negative aspects are that you`re bound to the PC and can`t port to Xbox 360 / PS3 or Wii. iPhone will be possible in near future according to the programmers of the engine.
I would recomment to start with GameStudio with the free version. By doing this you can learn the workflow and the lannguage. If you don`t like it you will have an easy time to switch over to other game engines because Lite-C is nearly the same as C or Java.
Gamestudio enabled me to program a working Unreal Tournament like game nearly completely by myself! If I would have used other engines I needed twice the time for this big project I think.

@all: I personally like WED. I use it for building UT-like block levels and really can`t complain about it. Okay, it would be very nice to have a working build-and-watch-in-wed feature to check the lights but hey, I paid 170€ for a software three years ago that enables me to make games in the quality of Adrenaline as a one-man-team at the moment. I really can`t complain about Gamestudio. Like I said it`s much more stable and transparent than most engines out there. I`m really happy about it!