I don't like it for a reason that it multiplies exclusive titles. I consider it a failure. Normally authors should aim to reach the most audience, not to exclude users because they use a different OS. This API will proliferate the later.
A failure is something which doesn't succeed in achieving its goals. We often approximate this by looking at how widely used something is. For an API, this measure seems reasonable.
It has nothing to do with your views on vendor lock-in.
Direct3D also causes lock-in. That doesn't make it a failure.
