The main purpose of the MVC (Model, View and Controller) architecture is to make separation of the business layer (logic) and the application layer (data)  from the presentation layer to the user.

Difference between MVC2, MVC3 and MVC4
View Engine :View Engine is responsible for rendering of the HTML code from your views to the browser.
MVC 2 uses only Web Forms view engine (.aspx) as a default View Engine.
MVC3 uses Razor View Engine (.cshtml for c# and .vbhtml for Visual Basic) and Web Forms view engine (.aspx).
MVC4 also uses Razor View Engine as a default view engine with some new features like condition attribute and ‘Tilde slash’.
Chart, WebGrid, Crypto,WebImage, WebMail Controls :
All these are not available in MVC2.
All these are available in MVC3 and in MVC4.
Syntex :
(HTML Syntax) Web Forms view engine syntax: <%=Html code %> in MVC2.
(Razor Syntax) Razor View Engine syntax: @Html code in MVC3.
MVC4 has the same Razor View Engine Syntax but with the addition of new features like conditional attribute and ‘Tilde Slash’ i.e. URL resolution.
Objects available for sharing of data between View and Controller :
TempData, ViewData are available in MVC2.
TempData, ViewData ,ViewBag are available in MVC3.
TempData, ViewData ,ViewBag are available in MVC4.> TempData is used with current and subsequent request i.e. when you know the next view to be redirected.

> In ViewData, dictionary of objects are accessible via strings as keys.

> ViewBag was added in the C# 4.0 which uses the dynamic feature that allows to add properties of an object dynamically . We can say that ViewBag = ViewData + dynamic feature around the ViewData dictionary.

Jquery Support :
Jquery support is Good in MVC2.
Jquery support is Better in MVC3.
MVC4 provides better support for Jquery like Jquery Mobile.
Dependency Injection Support :
Dependency injection is Good in MVC2.
It provides powerful hooks with Dependency Injection and Global Action Filters in MVC3.
Better support in MVC4.
Layout Support :
Supports only Master Page in MVC2.
Supports not only Master Page but also Layout Page in MVC 3 and in MVC4.
Validation :
Client-side Validation and Asynchronous controllers is there in MVC2.
Unobtrusive Ajax and Client side Validation, Jquery Validation and JSON binding support is in MVC3.
Client side validation, Jquery validation and enhanced support for asynchronous methods in MVC4.
Project Templates :
MVC3 supports project templates enabled by HTML 5.
MVC4 supports many new features for mobile apps and also provides new mobile project template and default templates are refreshed and modernized.