What's New in ASP.NET 4.5 and Visual Studio 2012

· ASP.NET Core Runtime and Framework

· Asynchronously Reading and Writing HTTP Requests and Responses

· Improvements to HttpRequest handling

· Asynchronously flushing a response

· Support for awaitand Task-Based Asynchronous Modules and Handlers

· Asynchronous HTTP modules

· Asynchronous HTTP handlers

· New ASP.NET Request Validation Features

· Deferred ("lazy") request validation

· Support for unvalidated requests

· AntiXSS Library

· Support for WebSockets Protocol

· Bundling and Minification

· Performance Improvements for Web Hosting

· Key Performance Factors

· Requirements for New Performance Features

· Sharing Common Assemblies

· Using multi-Core JIT compilation for faster startup

· Tuning garbage collection to optimize for memory

· Prefetching for web applications

· ASP.NET Web Forms

· Strongly Typed Data Controls

· Model Binding

· Selecting data

· Value providers

· Filtering by values from a control

· HTML Encoded Data-Binding Expressions

· Unobtrusive Validation

· HTML5 Updates

· ASP.NET MVC 4

· ASP.NET Web Pages 2

· Visual Studio 2012 Release Candidate

· Project Sharing Between Visual Studio 2010 and Visual Studio 2012 Release Candidate (Project Compatibility)

· Configuration Changes in ASP.NET 4.5 Website Templates

· Native Support in IIS 7 for ASP.NET Routing

· HTML Editor

· Smart Tasks

· WAI-ARIA support

· New HTML5 snippets

· Extract to user control

· IntelliSense for code nuggets in attributes

· Automatic renaming of matching tag when you rename an opening or closing tag

· Event handler generation

· Smart indent

· Auto-reduce statement completion

· JavaScript Editor

· Code outlining

· Brace matching

· Go to Definition

· ECMAScript5 support

· DOM IntelliSense

· VSDOC signature overloads

· Implicit references

· CSS Editor

· Auto-reduce statement completion

· Hierarchical indentation.

· CSS hacks support

· Vendor specific schemas (-moz-,-webkit)

· Commenting and uncommenting support

· Color picker

· Snippets

· Custom regions

· Page Inspector

· Publishing

· Publish profiles

· ASP.NET precompilation and merge

Source : http://www.asp.net/vnext/overview/whitepapers/whats-new

We will see each feature one by one in details.