It's pretty great. Dark Souls with guns is very accurate. There are TONS of secrets to find, and several awesome hidden classes that you can swap between once you unlock them. I've been playing as Gunslinger so far, and he's really really good.
That said, I almost rage quit the game early on lol, as you're pretty underpowered at first and checked out a side area early on that has some glitched enemy spawning on my campaign roll.
Everything is procedurally generated and your campaign can start in any world, so it's possible that others won't run into the same issue. In the Council Chambers area of Losmon, I had instances of enemy packs spawning behind me with a particularly annoying elite, and also duplicate spawns of the same enemy wave, which created a pretty crazy difficulty spike.
Once I got past that area, however, I haven't run into any similar issues and have been really enjoying the game as my character gets stronger. Can definitely recommend.