A couple people i know started talking about it at that point, and i ended up checking out a videocast/Let's Play of it (https://www.youtube.com/watch?v=MZ6jJBoCfO4) and ended up deciding to get a copy (for the full $15.)
So the general concept is combination roguelike and rhythm game with 16-bit graphics and music.
Each level has it's own song. The songs all have a strong rhythm and beat and some of the UI elements pulse in time the beat. There's also a meter at the bottom, a beating heart with a series of vertical lines converging on it in time to the beat. Pretty standard rhythm game stuff except it just signals when the beat happens without specifying a particular action you need to take.
You only use the directional keys during play. Everything you do in the game has to be done in time to the beat using the four keys. When you kill an enemy your boost multiplier goes up. The main effect of that are that all enemies drop more gold, and the grid that makes up the floor start flashing in an alternating pattern in time to the beat, which kind of makes it look like a disco. From that point on if you ever fail to take an action on the beat you loose your boost.
When you press one of the key the game automatically determines what action to take. Generally if it's an empty space you'll move in that direction. If there's a wall in the way you'll try to dig through it. However if there is an enemy in range of your weapon you will attack instead, which is where things start to get tricky.
At the start of the game a lot of enemies die in one hit so they're relatively easy to take out. However you start the game with a dagger, which can only strike the space immediately next to you. All the enemies have specific movement patterns that you need to learn. A few enemies move one space toward you every turn, others have a pattern that consists of one or more turns of movement, either toward you or in a set direction, followed by one or more turns of inaction. If an enemy moves into your space, either because you're standing still in their path or both of you try to move to the same space, you take damage. So you have to time your movement so you both arrive at a spot next to each other on the same turn so you can attack, or you have to approach during one of their periods of inactivity. Which sounds pretty simple in theory...
The overriding complication is the necessity of doing everything to the beat. When everything is going well and you're moving to the beat it's a good feeling, which is the primary attraction of the game. When you run into a complicated situation however you have a very limited amount of time to think between the beats and it's easy to get flustered and either take too long thinking and miss the beat or make a snap decision that turns out to be wrong. Given the forced timing it's not uncommon to commit to an action and realize even as you're carrying it out that you just did the wrong thing.
When you're facing a single enemy you can always just hop back and forth between two squares while you consider your options or retreat while the enemy follows you until you've got a plan of action. However when you get into a situation with several enemies in close proximity and you need to consider all their moves in conjuction you're again in a situation where it's easy to get flustered.
As you get further into the dungeon you encounter enemies with more than one hit point and you find better weapons, both of which offer further complications. With multi-HP enemies you have to think about their patterns more carefully because you can't jump in range for a single strike and finish them off. Your hits take precedence, but if they survive your blow it's entirely possible for them to hit you on the same turn. Better weapons generally don't increase damage they increase range. Spears hit the two spaces in front of you. Broadswords can hit multiple enemies in a 3 square long line perpendicular to the direction you're facing. Whips have a similar pattern to boardswords, except it's a 5 square long line And it only hits one enemy at a time. Etc.
In general this is of benefit, especially when dealing with enemies with lots of HP like bosses. (I've had to fight dragons while wielding a dagger on a number of occasions. It has never worked out well.) However remember that the game automatically decides your actions based on the current context. You need to keep the weapon you currently have equipped in mind while watching the context around you or at some point you will try to retreat from an enemy that's right next to you only to find yourself attacking some other enemy instead while getting stabbed in the back by the first enemy. Even in less dire situations when you're planning out your moves in time to the beat expecting to have one thing happen and getting a different and unexpected result can really throw you off.
Along with new weapons you will also frequently find other equipment, better mining equipment to dig through different kinds of material, armor to absorb damage, helms and rings with various effects, and usable items. Since there are only 4 keys used in the game in order to consume or activate items you have to press a combination of two keys. It seems that consumable items are left and up or down, spells are right and up or down, and up+down to switch weapons (if you've got the right equipment for that.) Learning how to do that without losing the beat is also a little tricky.
When you start the game you go through a brief tutorial first consisting of a couple rooms. After that you go to the main hub area. I believe at first you can access the Zone 1, the daily challenge, the "hardcore" mode, and the "easy" mode for dance pad users. Zone 2 and Zone 3, all the hub stores, and possibly a few other things are locked to start.
Zone 1 puts you in a dungeon similar to the tutorial, except obviously larger. There are three levels to the zone, followed by a boss fight. Thee levels generally consists of... 5-6 main rooms maybe? So not especially large. Which is important because when the song ends (after about 3 minutes) you're automatically dropped to the next level. When the song is nearing its end the tone changes a bit, and more importantly the marks in the beat meter at the bottom turn pink.
Frequently at the start of the game you'll find someone locked in a cage in one of the rooms. If you find the key and release them a new shop opens up in the hub area. (There are 5 you can unlock immediately, but there are more locked doors that i haven't gotten open yet.)
Every level also has a store somewhere in it. Store consist of rooms made out of gold bricks with a shopkeeper inside who has three items for sale. (Note: If you have any bombs you can detonate them in a corner of the shop to blast the walls into gold coins.) You can see the items and the price but nothing else until you buy them, and once you do you get a brief flash of the name of the item which is usually somewhat but not wholly informative. So you have to either experiment with items a bit to figure out how they work or look them up online (which you obviously can't do very easily while playing) but appearance is standard, not randomized, so once you learn how a particular items works you can identify it in the future if you remember.
There are also diamonds in the dungeon, sometimes in the open, sometimes hidden in walls (with a small sparkle to give them away if you look closely.)
When you finish the dungeon, either by dying or beating the boss, you can go back to the lobby and spend your diamonds on upgrades at the shops you've opened up. Any diamonds you don't spend before starting your next run are lost. The most important upgrade to get at the start is of course extra heart containers. However you can also increase the number of chests that appear in the dungeon, buy better weapons and items and spells (which are added to the random mix of chest loot) and increase your base gold bonus.
When you beat the boss of Zone 1, Zone 2 is unlocked. I have not done so yet but presumably Zone 3 is unlocked in the same way.
Instead of being an underground dungeon Zone 2 is some kind of mossy/fungusy area with new and harder enemies.
I have not tried it yet but in the "hardcore" mode (i forget if that's the real name or not) you start in Zone 1 without any of the permanent upgrades you bought, and when you beat the boss you go straight on to Zone 2. In addition to providing a more of a challenge this is also a way to accumulate more diamonds. (I'm quickly reaching the stage where there are a number of items i can't aford after a run through Zone 1.)
I think that's about all the nitty-gritty details.
So far, after 2-3 hours of play time, i've found Zone 1 to be very fun. I like the atmosphere, i like the combat, i like the music.
Zone 2 is... a challenge. And i mean that both thematically and gameplay wise. I personally don't find the style of music for Zone 2 anywhere near as interesting, and the enemies have much more difficult patterns. And they're generally tougher, which can be a problem since you start it equipped only with a dagger. So generally Zone 2 is a short period of time before i die spent listening to not particularly engaging music.
I may start trying the hardcore mode so that at least i'm going into it with some decent equipment. I may also try replacing the default Zone 2 music with some of my own music, an option that i have not tried up until now so i can't really comment on how well it works.
Going by the soundtrack the music style picks up again in Zone 3, so if i can make it through to that i may enjoy that section more.