Compared to its Windows 8 counterpart there are some features it simple does not support because Windows 7 does not provide the underlying support needed for the feature or does not enable it to the degree Internet Explorer needs for optimal experience. And if you think about it, Windows 7 is now a 4 year old operating system and simply does not have some of the necessary plumbing included in Windows 8. These features include, with some of my commentary:
- Device Orientation events - probably not included at the OS level as Windows 7 was the last Windows designed without core support for mobile features like orientation.
- Drag and drop touch support - again, Windows 7 was not really designed for touch
- Effects batching and stroke improvements - while Windows 7 has good Direct2D support it is probably behind 8. Chrome suffers similar issues to my knowledge
- Encrypted Media Extensions - Again this is something completely new since Windows 7 was created
- Enhanced Protected Mode (EPM) - again a concept that was created well after Windows 7 release
- F12 developer tools UI Responsiveness - The UI responsiveness tool probably relies on graphics drivers and simply requires your Windows 7 to be updated to the latest version according to the documentation.
- High DPI support - The current high resolution monitors and displays were not common 4 years ago
- Hover touch support - Again relies on OS plumbing that simply was not included in Windows 7
- Link highlighting - Again a touch friendly feature
- Media Source Extensions - Another modern standard that was either not ready as a standard or maybe not even started when Windows 7 released
- Phone number format recognition - Windows 7 was not designed with the concept of making a phone call natively. The concept has proliferated with the rise of mobile since then.
- Pinned site enhancements - Windows 7 does not have live tiles and Windows 8 does. You can support live tiles with IE 11 and traditional pinned sites with Windows 7
- Screen Orientation API - Again Windows 7 was designed as a fixed desktop OS, not a mobile first OS
- Scrolling and zooming with touch and other inputs - touch...
- Syncing across devices - Another relatively new concept, it does seem this should be OS independent though
- TCP Connection Sharing (SPDY) - SPDY is just a couple of years old as a common standard and still slowly gaining broad support.
As you can see just about every missing feature is due more to Windows 7 age rather than Internet Explorer. So please take into account these missing features are primarily mobile related or implementations of standards and concepts that simply were not developed or stable at the time Windows 7 was released and typically rely on underlying operating system support to make them happen well or at all. You can read more about Windows 7 compatibility issues here.
And as for things you do get, WebGL for one. Now you can play WebGL games like Hover. There are also many underlying performance improvements. Some other improvements include FullScreen API, Flexbox and border image. As for performance more than likely Internet Explorer passes the latest Chrome and FireFox. Check out Craig Buckler's Internet Explorer 11 review to see several performance benchmarks compared.
As someone who has been using Internet Explorer 11 for few months now I encourage you to upgrade. As a web developer I beg you to upgrade! Internet Explorer 11 is one of the fastest browser available and I often test sites and find they are faster in IE 11 than another other browser, and I use them all. But more importantly you are gaining new feature support, improved security and of course new developer tools.