I'm sure Unity can make such an RPG. I looked at the trailer and don't see anything too far out of the ordinary. Now that doesn't mean it won't take some work. You would have to learn the programming for it, and the art, etc...
Unity doesn't directly support C++, rather C# is the most commonly used language with Unity, though they offer Unityscript and Boo as well. If you are interested in using Unity, I'd recommend it. But, GameMaker: Studio also has a free version. I think it too could handle most of what Child of Light does. It isn't as advanced as Unity, but it is much easier to learn. You can use a drag & drop interface for some of the scripting, but I'd say you are better off learning GML, which is a C-like language GameMaker uses for scripting. There are some things that GameMaker can't do, and if you want to deploy to mobile platforms you will have to pay for those versions. Unity on the other hand, in the free version can export to iOS and Android. The catch is that the exports are limited in some ways though not as much as people think. The other catch is that like I say, Unity is harder in general to learn than GMStudio is, and that includes the scripting language.
In the long term, Unity may be better for you to learn. It isn't meant for 2d games exclusively, and GMStudio is generally better at 2d games than Unity. There are some things Unity can do with 2d that GMStudio can't, especially things that involve breaking into 3d for effects, etc... But, GMStudio at the moment is basically crap if you want 3d. It can do some things, and shaders can be created and used for things as well. But, there is no 3d editor, and the only 3d support is from addons/extensions from the computer for the most part. So basically, if you are interested in 3d games, you will be better of with Unity in the long run, assuming you only want to take the time to learn one tool that can do both things instead of the overall best tool for the job.