I am a huge fan of the work that Ubisoft has done with the Rayman (especially Ryman Legends game) game engine. (http://ubi-art.uk.ubi.com)
If you want to see some behind the scenes work with their engine I have videos saved here on my Pinterest board.
(https://www.pinterest.com/nickzucc/ubisoft-2d/)
So I set out to see if I could get a similar look/workflow going in UE4. (2.5D Game Art in UE4)
Here are the results of my investigations.
Here you can see in engine if I break the game camera and look from a more 3/4 view you can see the layering of the elements.
Here is a matinee video that I captured from in engine to show off what the level is looking like with the modular 2D pieces:
All the work was done in Maya, Photoshop and UE4. If you would like to take a look at how the art was created, exported and set up in UE4 I have some videos for that as well.
If you are curious as to why I might be sharing all of this, well it is pretty simple. I love old school side scroller games, and I know there is so much that we could do with this genre given today’s hardware and software. I love the UE4 engine, but I do feel that if the engine were to really support these types of games (2.5D) then there is still some work that needs to be done. I really think the paper 2D stuff is very cool…but me personally, I think the 2.5D is where it is at to get the best of both the 2d and 3D world. As much as I love 3D I can’t wait to see what artist do when they get the correct tool set in their hands to easily take their 2D art skills and translate them into living interactive worlds. So my hope is that by sharing this work with the community, it will spur other artist to think about using the engine in this was as well! 
https://youtube.com/watch?v=s3UugtF1ktc
