How deep is it compared with other genre titles? And how far into early access is it? Does it feel like a complete game?
It is definitely not as deep as something like Tales of Maj'Eyal but has enough complexity to be interesting for players experienced with the genre while being (somewhat) welcoming for new players. It has all the staples you would expect like unidentified potions/scrolls, varied classes/skills, lots of death, plenty of loot to find and turn-based combat. The UI is shaping up to be MUCH better than other roguelikes though which is always a big gripe for me; I think bad UI adds faux complexity in a lot of cases.
The comparison to Rogue Legacy I mentioned before is one of the things that really sets the game apart. You find various objects throughout the world from tough monsters that allow you to upgrade your Academy. Upgrading your Academy let's you do things like have all Tier 1 potions identified when you find them, provide extra stat points, and so on. All of these upgrades can be accessed immediately on a new character so you keep making progress or you can eschew them and just head out into the world.
The game also features an overworld where you travel between dungeons and towns. It adds variety to the game and makes the game feel more interesting rather than just jumping straight into the dungeon every run.
As for it feeling like a complete game, it still has a couple months to go I would say. There is still a ton of balancing/polishing happening, features being implemented, art being created and so on. You can check out the current bug list and roadmap with the status of everything
here. The dev has been really good about updates and progress so I have no worries about this one getting done and being an even better game post-Early Access.