I recommend learning MVC, but that's just because I prefer the request/response concept of the web without having to concern myself with Microsoft-ism's like Page Lifecycle, PostBack, and ViewState. Most MVC fans will tell you that these details were Microsoft creating problems that didn't exist.
The ASP.NET WebForms model was designed to get WinForms developers to write for the web, and it's just ugly (again IMO). Control-style structures are a bit of an antithesis on the web.
MVC is open source, but open sourced by Microsoft. Just because you can download the source code from Codeplex, it's not really open source the way a jQuery plugin, Fluent NHibernate, Ninject, StructureMap, etc. is open sourced.