Asp.net webapi is quite good, I have to say!
The sad thing is that even ASP.NET MVC- which is 100x better than WebForms- is used 0.001 as much. The same fate may apply to the Web API. It just doesn't seem like there is much interest.
i would have thought ASP.NET MVC is quite mainstream and that webforms is slowly dying personally...
now with webapi and a pure html client, i see no point in MVC whatsoever!