I like Roguelikes. I like the randomized levels, I like the brutal but generally fair gameplay, I like the feeling of slow but genuine improvement as you fail a little bit better each time. (If you have no clue what I'm talking about, go look at the articles I wrote for Spelunky, or Dungeons of Dredmor, or Shoot First, or Desktop Dungeons, and you'll get the idea.) I also like free games that experiment with something new. So, even in a slightly rough, unfinished state, Delver makes me very happy indeed.
Coming as so many good things do from TIGSource, Delver is "a first person action roguelike"... an attempt "to combine the mechanics of games like Ultima Underworld with the depth and replayability of a roguelike." In practice, right now it plays a little like Doom, a little like Nethack, and a little like The Legend of Grimrock. Which, itself, plays like a lot of old classic games. Here's a video where the designer speaks for himself a bit:
I've only done a couple runs through Delver so far, but there's a lot I like about it.
It isn't entirely without its problems - there are still some bugs in there, like combat sounds disappearing when I enter a new level sometimes, and I don't like how random the enemy respawning seems to be. It is in the flavor of Roguelikes to have enemies respawn, but in this it seems like a room I just cleared can suddenly have bad guys in it when I go back in, and that's aggravating.
That won't end well for anyone.
Still, I expect I'm going to spend quite a bit of time with Delver. It's still being actively updated by developer Chad Cuddigan - the latest build is only a few days old, and apparently he's working on getting bows & arrows working the way he wants now. If you like it enough to toss him a couple bucks and you have an Android device, it's also in the Google Play store for $2, which seems quite reasonable to me. (It looks pretty great on my Nexus 7.) The Windows version is totally free, though, so get delving.