There are many more items on the list for ASP.NET 4.5.1, but the update to the Identity system is a big one. The Membership Provider System added with .NET 2.0 was a great new feature, but a great deal of water has passed under that bridge since then.
The new ASP.NET Identity system, sometimes referred to as One ASP.NET Identity, preserves the old options of being able to store credentials in a SQL database, but adds support for testability, social media authentication, and claims-based authentication.
#!C++ continues toward the mainstream
Microsoft has its promise of working to catch C++ up to the other languages, with features such as auto complete for closing braces, such as parentheses, curly braces and square brackets. Other features developers in C# and VB.NET take for granted are better code formatting, improvements to Find All References, and a resizable properties window. Many others would have undoubtedly evolved if C++ had been maintained over time as C# and VB.NET have been maintained and improved.

There are also enhancements that make C++ better for Windows Store development, and the addition of a REST SDK. As with past versions of Visual Studio, there are a bunch of other updates that are very niche and too numerous to list, but many of the C++-related ones are focused on faster speed in either the resulting code or the development environment. C++ already has a reputation for the best language if speed is your primary need, and it looks like Microsoft is going to maintain that aspect.

A whole lot more
As we have seen, there are a number of interesting new features in Visual Studio 2013, even though it does not have as many new features as some previous releases. But there are still too many to detail completely here. Regardless of how you use the development environment, there are a number of features that should be of great interest, such as Edit and Continue support for 64-bit applications, and the fact that MSBuild is now being included in Visual Studio instead of as part of the .NET Framework.

The key to enjoying any new version is to check out the edition comparisons provided by Microsoft to ensure the features you want or need are in the edition you have or are looking at. This will prevent disappointment like that associated by the choice about CodeLens.

It was a bit of a surprise to see that the Professional edition includes features like Architecture Explorer, as well as collaboration features like Code Review and PowerPoint Storyboarding. Normally these kinds of features would be expected to only exist at the Ultimate level. Overall it would probably have been a better choice to move these items to Ultimate, provided CodeLens could be brought into the Professional edition.

With Microsoft seeming to be releasing everything on a faster cadence, it might not matter so much as they can switch things around and expand these features to lower-end editions with each release.