Why some people wants to kill Opengl to replace it with Mantle a not Open source, bad documented, Amd GCN bounded API that ,in spite of being an api that works only with a small sets of cards (AMD GCN), in some cases causes stutter, vsync problems and crossfire problems, so it's just some kind of beta right now.

On the other hand Opengl can give developers the same performance gains that mantle claims with support for all the major vendors (Amd, Intel, Nvidia and even some Mobile phone gpus) it's open source and already exists.

Some GDC 2014 Slides: http://www.slideshare.net/CassEverit...iver-overhead#