I also doubt very much ID will let you use it for commercial purpose for free.

That's out of their hands, now, which was the whole point of GPL-ing it in the first place. Whether people would pay for a GPL game, I don't know.

[quote name='Dunge' timestamp='1331070871' post='4919902']
I also doubt very much ID will let you use it for commercial purpose for free.

That's out of their hands, now, which was the whole point of GPL-ing it in the first place. Whether people would pay for a GPL game, I don't know.
[/quote]

There are a few ways around that though, You can sell proprietary assets (This might be a gray area as some assets could be considered a derived work of the engine and thus fall under the GPL), access to online services, etc instead, You'll still be forced to compete with free alternatives created by the community though. Trademarks are also not covered by the GPL (While this doesn't necessarily prevent people from sharing your game for free it will prevent others from selling your game using the same name).

Its kinda hard to recommend a GPL licensed engine for commercial games though when there are tons of other engines on the market that are just as good, cost $0 or atleast very little and place far fewer restrictions on the developer. (If it was easy to come up with a solid businessmodel that didn't suffer from free redistribution of the game then piracy would be a non issue.)

I don't know if you are looking for a game engine or a render engine. If you're looking for a game engine, you might want to take a look at Unity3D if you don't mind switching to C# (and live with the "limitations" of the free version), and as till the 8th of april, Android and iOS licenses are free. In my own experience, Unity3D is the only thing that comes close to comfortable when it comes to game engines (that are free!)

If you are looking for rendering engines you can also take a look at Ogre3D and Horde3D. Ogre3D has been around for some time and has great support and the tutorials are pretty much up to date. It is however a pretty bloated engine with features you might not want to use, but if you know what you are doing, this will not get in your way.

Horde3D is in comparison to Ogre3D very lightweight and pretty new. The last time I used the support was good, though not as quick to reply as with Ogre3D, but good nonetheless. I don't know if things have changed, but a lot of their tutorials were outdated as they focused on the new version to bring out, this could have changed though and there is enough that remained the same to get you started.

You can always use some middle-ware for the physics like PhysX, Havok, Bullet or Ode to name some.

As for skeletal animation, I don't know what format you'll be using, but perhaps this will come in handy: http://3dgep.com/?p=1053
It's for MD5 models, but it should give you an indication on how to do it with other formats.