Of the Dungeon Crawlers I've played (I haven't played many, because mindlessly killing enemies just never feels interesting to me... I like a reason to do so beyond gaining levels), here's the (short? long?) list of things that I've personally enjoyed about them.
1. Multiplayer. Honestly, I vastly prefer when a dungeon crawler is "multiplayer" as opposed to singleplayer. If it's singleplayer, I'll pick the single most optimal path through the game, play the game once, and then will be done forever. If I finish at all. If it's multiplayer, then my friend and I can pick different things, impose different rules, and generally just make the run "more enjoyable" that way. While Wasteland 3 wasn't a "Dungeon Crawler", it had mechanics I really enjoyed, which I wish had ended up in future Dungeon Crawlers. Namely, the ability for the other player to create their own characters and so you could create a single "unified team" by having two players contribute to the same party. I created a Shotgun Medic. Why? Thought it would be fun. My friend made a Melee fighter who specialized in explosives and demolitions. Why? No idea. Said melee character also became a master merchant later too. My Shotgun Medic also eventually became really good at lockpicking. But, I have played multiplayer dungeon crawlers (like Path of Exile or Champions of Norrath) where each player picks their class and plays through the game. I like that too. Brings a lot of replayability and the ability to sort of edit your character as you go so that you compliment each other. This leans into #2.
2. Options. I like options. I hate how many there are in Path of Exile (makes charting a list of what you want to do and how to do it nearly impossible, it's so vast and weird and interconnected). For example, if I can be a mage, I like the ability to decide what sort of mage I'll be. Do I want to just be a fireball slinger? Maybe I want to cast plague or poison spells? Maybe I want to deal in acid and necromancy? I like options. The ability to customize what I've got matters quite a lot to me. I don't mean just a few options either. Generally speaking, I want the ability to tailor a character to specific purposes. Oh, I can't make a thief into a "Critical Hit" thief that does nothing except land criticals? Eh. I can't play a Ranger that engages in dual swords AND pet mechanics? Eh. I like to know there's multiple ways to run a class and each is it's own "playstyle". Or, that I can "mix and match" what exists to create my own playstyle. After all, I find it more interesting if a game lets me be a "magic tank", where I have a character that lets me run out to the front lines with Sword and Board... but he draws all the magic attacks to him and they do next to no damage to him, because that's the way he rolls. That's more interesting than "let enemies whack me with swords and sticks and just eat the damage". I like stuff like that. So, the more I can do interesting stuff like that, the better.
3. I need a reason to play. Look, it's not enough for me to "level up". It's a tired progression system that has rarely meant anything to me in all my long history with video games. Unless a level granted me a significant change in power, then I've largely not cared about it. If it has granted me a significant amount of power, I've used that power to over-level the content and steamroll the rest of the game (because devs rarely ever balance for anything beyond numbers, which is hilarious, and stupid). The story of a Dungeon Crawler doesn't typically grab me either. Mostly because... they're just generally not written very well. They can't be when the main objective is "wade through thousands of enemies to get to the one thing you're trying to do... if you don't wade through thousands of enemies, there's no game, so nobody can have 2 brain cells in the plot". No, what I need are extra things to be doing. A checklist, most often. Different rewards helps too.
Here's my off-hand example of what I'd like to see.
"Kill 30 Dire Bats to unlock 1 extra skillpoint"
"Use Fireball 300 times and it grows in experience"
"Beat the game with the Thief and unlock a new Trait for all future characters to use".
"Complete all the quests in this area to grant 3% better drop chances for the rest of the game".
"Reach level 25 with the White Mage and the Black Mage to unlock the Time Mage".
"Do this long quest chain across most of the game in order to unlock a second earring slot" (this one is actually in the second Champions of Norrath game, and it was fantastic to unlock it)
I like extra bits to do. Things that will grant me some reward or power that I might like. Even extra options to play with. I've always liked when games did that for me. "Here's the game... but here's also this list of Challenges of other things you can do, too. It has rewards for doing them!".
4. "New Game +". If the game is significantly interesting enough for me to finish it the first time, I'm sometimes wanting to keep playing with my character and start the game over again. But, retain all the work I put in the first time. Look, I love this feature in a great many RPG's as it is. I loved beating the game on Easy, then taking my beefed out character into the hardest difficulty for a slightly easier time. Or, playing it again on the same difficulty with my maxed out characters and fully unlocked everything, to just roflstomp the rest of the game. That's fun for me in a lot of cases. It's cathartic to a degree. I also like rewards and incentives to do things differently on a "new game +" mode. If I beat the game with a Mage, Warrior, and Healer last time, maybe each grants me some new reward thing I can use for a new run. Some new trait or item or something, to make leveling the low levels interesting or fun. Oh, the Healer gave all my characters a 5% HP Regen, whether they're old or new? NICE! Oh, I unlocked a much harder version of the game to play with my maxed out characters that unlocks ultimate equipment? AWESOME!
I like an excuse to keep playing. New Game + is often a good way to keep me going. At least, if there's a reason to do it. Though, to be honest, being able to roflstomp all the early game stuff that gave me trouble is pretty nice in its own right. Probably why I actually put 5 runs into "Trials of Mana". It was fun using my overpowered characters to cakewalk pretty much the whole game while I leveled up everyone else to max level.
I'm a sucker for stuff like that.