GTGameEngine is still very young. This page lists some known limitations. For the most part this will list only the most major limitations. For general bugs and issues, check the GitHub Issues page. Every issue listed here is planned to be addressed in the future, but are usually longer-term.
Documentation, in particular the C++ and Lua references, are extremely lacking. Work on this continues, but there is a lot to do. Future plans are to add an in-editor reference feature where the C++ and Lua references are available from inside the editor without needing to go to the reference website.
A "reference editor" will be added to the main editor which will allow users to create and modify reference files. A tool will then convert the reference files to HTML for online access.
There is currently no effort being put into backwards compatibility. Backwards compatibility will probably begin when version 0.1.0 is released or when there is enough demand.
There is currently no networking functionality whatsoever. This is the biggest major feature missing from the engine right now.
No real-world or stress testing has yet been performed on the engine, so there is most likely quite a few lingering performance and efficiency issue still needing to be ironed out.
Of particular note, rendering performance and memory consumption are most likely the biggest issues.
There aren't many supported file formats for images, models and sounds. There are plans for adding more formats, but there are no plans on adding redundant formats that don't solve a problem already solved by an already-supported format. For example, it's unlikely the engine will add MP3 support because OGG (which is planned) already serves the same purpose.
Check the Supported File Formats section for more information.
There is a lot of functionality not yet exposed to the scripting environment. This is an ongoing issue that is constantly being worked on.
Support for debugging scripts is virtually non-existant. The future plans are to incorporate debugging directly into the main editor, with all of the normal debugging functionality you would expect such as call stack and variable inspection, break-points, etc.
Currently, particle systems are very bare-bones. Of particular note, there are not many emission shape and function options available.
Future plans include:
There is currently no support for setting up constraints between physics objects via the scene editor or even the scripting environment. This is a major issue that will be fixed fairly soon.