Not to undermine use of Multi-Item Edit, but if you want the real "old-school" Get Info window:
Select one or more tracks. Press and hold Option then Right-Click the selection. Choose "Get Info" from the contextual menu that appears. (Thanks, Paul J.)
No clue if there are plans to eventually drop it or even why it's still there.
[UPDATE: Actually, selecting the contextual menu or the File menu and then Option-Clicking on "Get Info" gets the job done.]
[UPDATE 2: iTunes version 12.1 removed the old-style Get Info window.]