i'm not sure what you mean by "truly open-source"; what "game engine options" are you referring to?
Software distributed under a license approved by the OSI. These licenses, as far as I know, place no limitations on the type of speech that can be produced with licensed software. To use CryEngine, the people who work at CryTek must not find any of your project's content "objectionable".
>what "game engine options" are you referring to?
http://irrlicht.sourceforge.net/
http://www.garagegames.com/products/torque-3d
https://github.com/id-Software
and many others; I'm sure there are big lists floating around. All of the engines listed here can be used even if the authors of the engine disagree with what you want to say, and I believe they've all been used in real, honest-to-goodness commercial games.
Irrlicht and Torque is good options for small indie games (actually there many more great engines for small games), but they still can't be compared with "big" commercial engines.
When you review the license, it is really not like this. Only games made explicitly for "entertainment purposes" can use the engine -- even "Serious Games", which I guess means games that may straddle any actual utility, are not allowed. Most likely Kerbal Space Program would be considered excessively "scientific" and not allowed to use CryEngine.
There's also a very scary clause that essentially says "if we don't like your game we can classify it as objectionable and withdraw your license".
This is a cool release from an academic standpoint, but should probably not be used by real people for real projects with the license as-is. There are many excellent truly open-source game engine options.