Hello Stavros,
The difficulty of the learning curve depends on the script module you choose and what your main study direction is (more scripting/coding oriented or visual arts oriented).
At the time being the Drag[en]gine has one script module (more will be included at a later time, possibly also C#): DragonScript.
This script module is balanced between coding and visual editing (using the various editors). For quickly pulling up a project or doing prototyping you can use
Behavior Elements which is kind of Lego-plugging together Element Classes. For example the
Example Application uses mostly Element Classes ready-made by the game engine and thus using little amount of coding. DragonScript is a high level language so coming from C#, Java or similar languages you have to adapt to some different design concepts while typical features like memory management, object handling or class/interface handling is comparable.
To create models you need Blender3D since this is right now the only application having export tools to create models with. This will change in the future and depends on what users do request/wish for (like what 3d-app to support or what file formats to support). The Example Application contains
models.blend you can examine. You need to export *.demodel files (3d-meshes) and optionally *.derig files (collision, physics). You can also create the rig files in the Rig Editor. For starting out this is most probably easier. If you know Blender3D already then the learning curve should be easy. Otherwise learning to work with Blender3D requires some time to examine online tutorials. I think the current version of Blender3D is easier to learn than older versions. But that could be just me being a long term Blender3D user.
To create skins for your models you can use the Skin Editor. The concept is different from other game engines in that it uses no node-system. Instead a list of physical material properties is defined and where their content comes from. The learning curve for this task should be easy.
With all this in place you can go on and create a world in the World Editor. To start out quickly you can use the ready-made Element Classes and modify their Properties. This learning curve should be easy for this task too.
You can then step forward by creating your own Element Classes. Creating element classes in DragonScript is not too complicated if you plug them together using Behaviors.
Writing your own Behaviors is a bit more involved but is the key to work faster and cleaner later on. This task is more of an Intermediate Level.
So all in all if you are coming from a Unity background certain things are more complicated while others are more simple. What goes for DragonScript having a look at (and copy from) the example projects should help you along the way. All in all Drag[en]gine (at the time being) uses less visual editing than Unity does. If this is a Pro or a Con depends on your background. Coders find it more of a Pro that the visual editing is not getting in their way while artists find it more of a Con that they have to touch scripts.
If you have more specific questions just hit me.