Both of those games use 3D graphics, with a mostly top-down camera. Most of the gameplay is probably two-dimensional, but the graphics are definitely 3D. You can use OpenGL or DirectX to render 3D graphics, or you can use a higher-level graphics engine like Ogre.

Or you could use a full on engine like Unity. Or Unreal. Or CryEngine. Or Source, which I think is what DOTA 2 uses. It mostly depends on how much of the engine you want to write yourself.

You could probably also make an entirely 2D MOBA, which would be very different graphically but could play mostly the same, similar to how Realm of the Mad God used 2D sprites to make an top-down bullethell shooter MMO. But I get the sense that you are looking for something that's along the lines of existing MOBAs.

I completely agree with ProtectedMode, going for such a leap will most likely turn into frustration, go for a smaller setup and learn how to make cool graphics in small steps.

If you are into C++ and would want to go to 2d first, I would suggest you to also take a look at orx (using it with scroll), I find it much more better than SFML.

Since you say you have done 2d already I would suggest learning a 3d engine like Ogre3d or Irrlicht. Don't try to write your own engine using low level api like directx/openGL. That not only would take a very long time for one person to write but require a very high skill level.

If you still want to hang around 2d for a while use sfml 2.

I would suggest you to also take a look at orx (using it with scroll), I find it much more better than SFML.

Are you sure this is a good choice? I've never heard about it, and for as I can see the community isn't that big. As I see you can use INI-files for initalization and such, I guess orx is a lot bigger and harder to learn than SFML or simular libraries.

The community is small but very active, I got answers to all my questions in a day or two. The tutorials are pretty good too, I have used both pygame and SMFL and I find orx is away better than both.

If you want an example, last semester I took a course on game development lab as a special student in the college which I am graduated (CS).

We had about 5 months* to do a game, here is my result:

https://drive.google.com/file/d/0B0UdeUM9pB-ndXlEdFM4Zm1hQU0/edit?usp=sharing

Personally I found that learning the ini system take some time by itself (not that much time, just be careful that the keys are case sensitive), but after you get the handle of it, you can create some special effects very, very easily (particle effects, for instance).

If you look at the video, the first arrow effect I created was the fire arrow, took me about 2 hours to learn how to use the particle system properly, all the others took me less than 5 minutes to create. The monster death effect also took me a few minutes.

That prototype have a total of 4039 lines of code and 904 lines of ini files, but I implemented somethings I didn't had to (such as lists and memory pools, which the library offer).

* Keep in mind that besides 4 hours of classes per week, I also work at a full time job (42,5 hours/week), so I didn't have that much time to work on it.

EDIT: Please notice that I am not an artist, so my effects won't be anything amazing, but that is not the engine's fault