[Edit] An option was added by the devs to remove the flashing! Now i've gotta come up with other things to talk about in the Review :D
I'm a really big fan of action roguelikes, so I'm quite happy to see more coming out and I instantly wanted to give this a shot.
My first reaction to seeing the trailer was to think that the game may be too derivative of The Binding of Isaac, but luckily I tried out the game and saw how wrong I was.
This game has a striking resembalance to The Binding of Isaac, as they're both of the same genre and are both seemingly inspired by older entires in the Zelda franchise. The similarites don't go too far though, as it appears that Isaac was based off of the original Zelda, with every room having exactly the same dimensions, whereas Diehard has more similarities to Zelda: A Link to the Past. The result is a much more organic experience, and your adventure focuses more on each unique room, rather than dungeon floors made up of maze of bland square areas.
The combat mechanics are also more developed, with the delver having a Zeldaesque sword for his primary attack, and a very interesting gun for his secondary attack. This gun shoots bombs, which can cause damage to enemies on both impact and explosion, but cannot hurt the player directly. The explosions of bombs push back both enemies and the player, and with the bombs propensity to ricochet around a room, it can make using it effectively quite tricky. This results in deeper, trickier combat mechanics than one would expect, and adds a certain richness.
A final added bonus Diehard Dungeon has over BoI is that it doesn't rely on blood, poop, tears and gore to have an atmospheric experience.
Overall it was a good experience, and with the low price tag the devs seem to be selling themselves short, though it does certainly help spread the love faster :)
While the gameplay was fairly enjoyable, the game overuses a visual effect which makes the entire screen flash white very quickly without warning. I play far too many videogames, and I'm virtually never affected by any kind of flashing lights(besides the seizure inducing flashes in Guacamelee!) but these flashes are definitely responsible for giving me a headache, and turning an entertaining experience into a negative one.
If this is patched out, I'd gladly give this game a thumbs up and would definitely give it another go, but at this point it's getting shelved after only a few runs.