The Goto Definition stuff is great.
The other feature I like in ST3 is multiple workspaces (under the project menu). Workspaces store the tabs you have opened (etc.), whereas project files define the project-specific settings like which folders to ignore.
I work on a largish Rails app with a single project file and a handful of workspaces. If I need to work on a section of our app again, I can reopen a workspace to continue where I left off, instead of tracking down a bunch of files.