the new gem system - there was this promise, that you don't have to roll fusings/chromatic/jeweller orbs anymore to make the sockets fit for your build on a certain item.
the graphical update - game looks phenomenal, let's be honest here.
Technical Upgrades on the engine - PoE1 has a shitton of technical debt and runs like ass. I was excited for them to be able to maybe start from scratch, or solve some longer lasting pains, that they never got around to with PoE2 (since the games ended up so different, that they drifted apart).
More smooth gameplay - I enjoyed the look of some of the older demos. It really seemed like travel skills felt more fluid and combat overall had more flow to it.

But honestly, I'm not really the right person to judge PoE2, I played roughly 10 hours in 0.1, almost finished Act 1 but then Life got a bit in the way and my playthrough fizzled out. From what I remember, monsters were too strong and too fast, playing melee kinda sucked (as is tradition).