I`m not a fan of quests, mid-bosses and other cRPG tropes in roguelikes. These could work if properly randomized but not always are, especially quests (old Sid Meier`s titles - Covert Action especially - did it really well). I`m playing lots of ToME at the moment and this is my major complaint about it - the "goal" structure is rigid, you always end up doing the same things, know where and what the midbosses are and don`t even bother with the lore scraps anymore.
It`s always been a problem with overworld type RLs - but at least in ADOM or Qud it`s just a line or two of text and the whole "quest" thing is not that important anyway because there`s much more to do and explore.
In a straight dungeon dive it could feel even more restraining than in an open world. If the mid-bosses are always in certain region holding the same thing the game risks becoming predictable and boring - and it also removes the important "fight or flight" mechanic - if the boss has a necessary item, it`s always "fight". (The whole thing kind of works in CRPGs because it`s tied to a story and you usually just play through once or few times between reloads).
I think approach from Crawl is much better - Sigmunds & Co can appear anytime, anywhere - sometimes two in the same room sometimes not at all (not played Infra Arcana too much so can`t tell for sure but I think The Witch -and maybe others - is appearing in a similarly random manner). And that`s what keeps you on your toes and makes the game more interesting. Same can be said for side-areas: why not randomize them and free from the mandatory quest carrot? If I see an entrance to a new place I will most likely want to explore anyway without some old sage ordering me to - and if my resources are low and/or general feeling not right, I might not. It`s a choice.
Overall, as a player, I`m not too bothered by having "goals", at least in the standard definition of. I think that`s what older RLs understood and why they just tell you to recover Amulet of X from down below - otherwise you`d have an infinite dungeon which is not that exciting. The most important goal in a roguelike, for me at least, is the gameplay itself - overcoming obstacles and watching plenty of interesting systems working together. Leveling up is one of these systems so yeah, it`s nice to be able to bump your stats every now and then and a valid "goal" too.