1) MagSafe. I know they really want to go all in on USB-C, but the original MagSafe connector was awesome. Even the weaker 2.0 version was nice. There were two instances where that connector saved my laptop.
2) The laser-drilled power indicator. That was so cool. It looked like the light magically appeared through the aluminum. Now there's no indication whatsoever if your laptop is on or asleep or off.
3) The 2007-2011 keyboards. The ones with the real travel. Even the 2012 version with slightly reduced travel was okay. But my 2007 MacBook had the best laptop keyboard I'd ever used.
4) HDMI and SD Card slot. These are the kinds of things that you happen to need when you least expect it. When you're least likely to have that dongle with you. They're also thin ports that will fit nicely without bulking up the chassis.
5) Of course, function keys and an ESC key.
I'm going to keep my 2012 MBP going as long as I can. But when it dies or is no longer supported, I'm pretty sure ThinkPad is where I'm headed.