Shattered Pixel Dungeon is one of like ten good Android games ever made (though you can play it on desktop just fine), and one of the even fewer good free and open-source games. It's one of several forks of the old Pixel Dungeon, but it's the most active and carefully maintained / balanced one, with a new class being introduced this year and regular patches.
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That is not to say that the game isn't open to a lot of discovery; the discovery is just more focused on items and mechanics. I strongly suggest avoiding the wiki at the start (it is extremely comprehensive and detailed) and accepting that you'll die a lot as you learn the game, because while not all interactions are fully explained in the game, none are particularly obtuse, and the "ah-HA!" moment when you figure them out is one of the best part of the game. Things like "I can throw this gross mystery meat on an ice trap to safely trigger it at a distance AND sanitize the meat!", or "I can pull piranhas out of water to insta-kill them". The boring stuff like alchemy recipes is available in the in-game quick guide, so you don't need the wiki for that.
Some key parts of balance are also fixed - you'll always find exactly 15 upgrade scrolls and 10 strength potions, for example, and just enough food will spawn to never take starvation damage if you do not waste time on sidequests (which you obviously want to do, so you'll have to find more food or deal with the starvation in other ways). As a result, hardly any runs are outright impossible if you master the game mechanics. At least with the base rules; the difficulty scaling takes the form of up to 9 "challenges" you can add, ranging from moderate (reduced vision range) to brutal (allergic to healing).
Typically, the biggest source of variety is the magic equipment you find in your early levels - artifacts, rings, and wands. Finding a +2 Ring of Sharpshooting in the first level will all but tell you to upgrade thrown weapons and focus on ranged skills - while finding it on level 18 after you already have a melee build will make you look for a Scroll of Transmutation to hopefully turn it into something more useful. But frankly, just beating the game with all six classes (which play very differently) will take you quite a while.
I freely admit that I'm pretty **** at the game, largely because I get overconfident and go "oh come on, I can beat this room with just regular attacks!" and then take like 40 damage when I could have taken 10 if I had burned a scroll or a runestone. But I've at least managed to ascend twice, once as a ridiculously tanky Berserker and once as an undead-master Warlock. Currently trying to learn how to play Huntress, which looks easy early on thanks to the bow letting you keep your distance, but gets tough in the endgame where most enemies have high mobility.