The best way to see what's new is to try the latest here. That's a 64-bit trial, if unlicensed. Some features may be disabled. A free version, with limitations, is here.
Many 'under the hood' improvements won't be apparent without speed comparisons between new and your old versions. Some hardware won't take advantage of them.
There are also new effects that vary from version to version. So play around with it. Retain your old licensing info and installer.