Free game engine that is really well documented and has good tutorials?

Engine: Unity.
Help & Tutorials: Unity forum, Internet, Youtube etc.
Platform Support: Mobile, PC, Web etc.
Supported "D's": 2D, 3D & 2.5D.
OS Supported: Windows, apple os etc.
Language Support: C#, [Javascript, Boo (or is it Unityscript].
Ease of Use: Said to be high.
Cost of Use: Free for 2d. Free for 3d (without some features). Paid. too
:)

Unity is really good, they have video tutorials on their website too.

If you love flash, maybe look at OpenFL?

That said, most of the biggies, like Unity and Unreal have pretty decent tutorial support, and forums and StackOverflow-esque question/answer sites. These big ones also have random people who post tutorials of their own. I followed a tower defense tutorial to get me started on Unity.

Are you looking to move to 3d or stay 2d? If the latter, you may want to look into something like GameMaker or Coco2d or one of the various HTML5 game engines.

Blender, it has a pretty decent game engine to work with. It's kept up to date, there are a lot of tutorials on the web for it, and it's quite to create game or even normal game for that matter in it. Hopefully I helped :).

When I think of good documentation, I think of commented and explained code, with complete examples, detailing simple as well as asoric aspects of the enginein such a way so as to pick up and program. That being said, I'm not sure there is such a thing. Just a lot of game engines with documentation ranging from decent to abysmal. Some better examples are Unity, Panda3d, and Irrlicht.

Blender, it has a pretty decent game engine to work with. It's kept up to date, there are a lot of tutorials on the web for it, and it's quite to create game or even normal game for that matter in it. Hopefully I helped .

Yeah, have fun with that one.

Torque 3d deserves a mention...

http://www.garagegames.com/products/torque-3d

Apparently it is now "free" per MIT license. I haven't used it in a long time...not sure about how sparse or rich the documentation is now. But its worth a look.

Unity & I must mention Cinder.. Both are easy to learn and get started ..

Ogre is 3d rendering engine, but what about it? You can still use other libraries for sound, input etc. I think its only better for you as u are getting better using more tools. I am no pro in engines, and I also look for engine myself :)

I use Haaf's Game Engine (HGE) http://hge.relishgames.com/

Its a hardware accelerated 2d engine.

There are tutorials and docummentation on site as well as entire source code available on their website even tho the last version is from 2008 it is completely free even for commercial use (except the included BASS sound library, which is free only for noncommercial use)

I just want to note that some of the listed game engines listed here are very small and/or dying.

Mixing multiple libraries together is probably not a good start for a beginner. I would advice a relatively complete library like SFML (you can look it up) or an actively used game engine like Unity.

But I think your question really depends on what you want. I myself started with GameMaker, which is a lot like Flash, but I liked more low-level things and the fun of coding with C++. But I can also imagine you could like having an engine to do all work for you, or use large libraries. These things, together with what language you would like to learn and/or know, are very important when making a decision about this.

I think you're overthinking it. If you see a nice engine with a good-looking tutorial for an engine, you should just try it out. As long as you have fun working with it, I would choose it, you can always learn more and other languages later. Just try starting here, nobody will argue that Unity is a bad game engine. If you don't like it, just try out some of the other engines listed here, or anywhere else! "Make games, not engines" (or something like that) seems to be a pretty popular article. I think an article called "use engines, don't discuss them" should also be written.