Guild Wars 2

When I left the game back in 2013 I had one of each class to level 80 with pretty much exotic gear compliments on each (wasn’t up for the grind for ascended).

Has enough changed since then that I need to spend time re-gearing or doing other “catch up” before tackling HoT?

I’ve been playing for less than a year, so I don’t know what mechanics changes there have been. I do know you can do HoT maps/story in exotic gear just fine. Raids (which will be released soon) are said to require ascended.
You will need a lot of hero points to unlock elite specs (not necessary to play expansion, but an unlock most people are working toward). The hero challenges on the new maps give 10 points instead of one, but are harder than those in the rest of Tyria (often champs).
Welcome back!

Welcome back!

I just got back to the game a few months myself. I made it through the HoT story using exotic zerker gear just fine. Roaming the new maps in zerker gear was hazardous at first, but you’ll learn what to avoid after a few deaths

For raids, here’s the dev tweet that recommended ascended gear. She also confirmed that agony resistance is not required.

And here are a few random pointers that players gave me on my return:
*All ascended gear is now account bound and can be used by all of your characters
*You can change the stats on ascended armor and weapons (but not trinkets). Recipe here.
*PvP rewards now include PvE items, so you can get dungeon gear or items from certain regions depending on which reward track you have active. Just another way to gear up if you find you need to make some changes.
*Minis are now stored in the wardrobe system. You may have some still in your bank collections though. They can not be put back into the bank collections once you take them out. (Check TP prices as I had about 100g worth of minis I sold off.)