I.... don't think I've admitted this to anyone on Gaf, but I..... haven't played Diablo 2. I played 1 a bit as a teen and a bunch of 3 more recently, but was pretty strictly a console gamer for the early/mid 2ks when D2 was at its peak. Probably one of my main regrets in gaming missing that.
Anyway, the games a spiritual successor to Titan Quest so if you've played that you should have a good idea what you're in for. I've also heard alot of people also say 'it's the sequel D2 deserves' and a large part of the community seem to have come across from it.
As for what to look forward to, it has insane depth with how you can build a character, with the ability to combine 2 classes, the devotion system, and some great supporting itemization. Want to wield a rifle and shoot lightening at everything, while lightening storms go off everywhere. Check . Want to dual wield pistols and build around that. Check. Want to make an assassin type character that zips around the map murdering everything with poison. Check. Sword and board. Check. Caster that shoots out all kind of magic out its arse. Check. You get the idea. While, maybe not quite as deep as PoE can get, it also doesn't require the same amount of absurd rng to get useful things, so its a little better on the self found front.
They've also done away with random level generators, and instead opted to build a well thought out hand-crafted world, that actually has a bunch of cool hidden stuff to find. Makes actually exploring the maps far more rewarding.
Tied to that, the lore in this game is actually really good. I ignored most of it at first, but upon further inspection its really well done. Its sort of the whole 'battle between heaven (aetherials) and hell (cthonics)' with the world you inhabit as the battle ground. But there's some really cool twists on that formula and totally worth paying attention too. Its very dark and brooding of course, but it has its moments of levity.
Also, as these game tend to go, 'the game doesnt really start until you hit Ultimate' (3rd difficulty). I'd argue it probaly really starts in the second difficulty as thats when you should see legendaries start dropping (level 50 and up monsters can drop them) and they of course change the way you play in some pretty significant ways.
Plus the
the devs did this once.. Probably the coolest thing I've seen a game studio do. It wasn't the fact that they did it per se, but if you look at the timing of the posts, it was acted on in around half an hour. So cool
As for a Hydra power, checking the wiki, the closest things would probably be lightening totems, which while kinda cool, probably aren't as rad as a fucking Hydra.
-edit- forgot to mention there an expansion due Q1/Q2 this year that adds 2 new classes, a new act of the story and a whole bunch more, so there's plenty to look forward to as as well.