Toys
Cyberjets - these guys are fantastic. Although they're pretty small by today's standards, their articulation was unprecedented at the time. Ball joints everywhere!

Predators & Turbomasters - Lot's of fluorescent yellow and pink clear parts for cockpits and windows, excellent light piping and some cool gimmicks with the Super Sight mechanism on the Predators. I read the Last Stand of the Wreckers comics recently and was super excited to see these guys show up. Such a shame very few of them made it to the end.

G2 Combaticons - I have a real soft spot for these toys. Sure, the colours are crazy, and there's no way that purple camouflage was ever going to work, but they have a certain charm and I think they actually look really good together.

Comic Issues/stories
- The entire G2 comic series was only 12 issues long. The first half is mostly tying up loose threads from the Marvel G1 series and the GI Joe cross over. The second half is where it really shines, issues 7+.

Cartoon Episodes/stories
Same as G1. I remember the CG intro seemed really cool at the time, but it definitely hasn't aged well. It had annoying little robot arm things that framed the picture and would animate the scene transitions too.

Slightly related, some of the advertisements for G2 toys are hilarious. The Superion + Bruticus and Dreadwing + Smokescreen are just fantastically terrible.