eBike technology explained

Hey everyone!

I've been looking at upgrading my old commuter ebike (a pretty basic hub-drive model) and diving into all the new tech out there is a bit overwhelming. I'm seeing terms like torque sensors, cadence sensors, mid-drives vs. hub drives, different battery chemistries, and even smart displays with navigation. What's one piece of ebike technology you think is a must-have or has genuinely improved your riding experience, especially for longer rides or hilly terrain? I'm trying to figure out what's worth the extra cash!