MVC 6
ASP.NET MVC and Web API has been merged in to one.
Dependency injection is inbuilt and part of MVC.
Side by side - deploy the runtime and framework with your application
Everything packaged with NuGet, Including the .NET runtime itself.
New JSON based project structure.
No need to recompile for every change. Just hit save and refresh the browser.
Compilation done with the new Roslyn real-time compiler.
vNext is Open Source via the .NET Foundation and is taking public contributions.
vNext (and Rosyln) also runs on Mono, on both Mac and Linux today.
MVC 5
One ASP.NET
Attribute based routing
Asp.Net Identity
Bootstrap in the MVC template
Authentication Filters
Filter overrides
MVC 4
ASP.NET Web API
Refreshed and modernized default project templates
New mobile project template
Many new features to support mobile apps
Enhanced support for asynchronous methods
MVC 3
Razor
Readymade project templates
HTML 5 enabled templates
Support for Multiple View Engines
JavaScript and Ajax
Model Validation Improvements
MVC 2
Client-Side Validation
Templated Helpers
Areas
Asynchronous Controllers
Html.ValidationSummary Helper Method
DefaultValueAttribute in Action-Method Parameters
Binding Binary Data with Model Binders
DataAnnotations Attributes
Model-Validator Providers
New RequireHttpsAttribute Action Filter
Templated Helpers
Display Model-Level Errors