I'm sorry this might sound rude, but let me get this straight. You copy and pasted in some NetEXT code and copy pasted in SFML.NET rectangle/vector classes all for the sake of "not confusing the user". Then you reinvent the wheel with your own drawable class (which looks more like an update class) all for the sake of trying to write a self contained library that hides what the library really doing internally for your little game dev community.
You also claim that the GUI used by your library is your own advanced code when you are really using Gwen. This really should be clarified, "Our GUI library makes endless possibilities in making of GUI for your own game" is extremely misleading.
To sum it up, you do your best to write your own library that hides the internal implementations from the user and prevents them from using the internal implementation directly in their own code. But at the same time you come to the community that powers your library and ask them to try your code that broken with the original library because you decided to copy and paste in code. It seems like an oxymoron to me, abstract away dependencies and then ask the dependency community to try out your code without directly using the dependency.
Not too good in my opinion, you can do what you want with the way you take my above comments. Remember its only the way I see it, but I don't plan on using any of your code since because as stated above, is broken with other libraries.
What I really would suggest you do is, #1 change the name - SFGL doesn't make much sense and is confusing, not to mention we just had this discussion over Lololilight's lib #2 don't re-implement other libraries code in your own library just because being self contained seems neat - in the end it just causes more headaches.
Oh and since you are up to 3 different "game engines" now I suggest you read the following link.
http://scientificninja.com/blog/write-games-not-engines