Hades is the game that finally got me to try an early-access release. I should explain: I generally feel you should buy a game only once it's been released and reviewed. In an era where physical stock is rarely a concern, pre-ordering games basically means you're giving publishers free money, but early access titles go a step further -- it's like paying to be a beta tester.
I can't claim to have jumped on Hades early, it's been out for more than a year. But I started playing it about a month ago, and it feels like Supergiant used the early access model perfectly. It's a "roguelike" action RPG where you battle through the depths of the underworld, trying to reach the land of the living, all the while dying repeatedly. There's a progression system where you can gain permanent bonuses, but most of your upgrades are found while playing, and are lost if you die. As with every rogue-like, you'll be seeing the beginning of the game a lot.
This isn't a new concept. But Supergiant, developers of the beloved brawler Bastion, along with Pyre and Transistor, has built on the combat from those previous games. It's created an exceptionally well designed system with weapons that feel unique; fluid and fantastic movement (especially dodging); and a difficulty curve that always feels just on the fair side of punishing. Depending on what upgrades you find, combat can feel totally different from one playthrough to the next. For example, a "boon" from the ever-helpful Artemis launches a seeking arrow whenever you hit an enemy. That power-up felt underwhelming when I ventured forth with a slow-swinging melee weapon, but it made me nearly unstoppable while wielding a rapid-fire cannon.
Supergiant centered the game in the world of Greek mythology, filled with bickering gods and memorable characters to create an actual narrative, something many roguelikes are sorely lacking in. Plus it features three-headed hellhound Cerberus, and he's the Goodest Boy in the whole underworld. (Petting Cerberus may be the most satisfying virtual-dog interaction I've ever had.)