As someone with maybe 5-10 hours in, and a meme-y/casual fan of the game rather than a hardcore player. Until/unless you overcome the UI (easier to do with a tileset mod like I'm using), it's not going to be enjoyable unless you like trial and error "What the hell is that symbol/does this key do/how does that thing work/WHY IS EVERYONE DEAD?!". Once you can get over that first hurdle, it depends on how much you enjoy learning the quirks and mechanics of a game in order to get better. Half of it's a learning experience about pretty much everything that can possibly happen, which can go on for as long as you play the game, and half of it's muscle memory with commands and queues and management. I RTSes a fair bit and am an avid SupCom player, so the management's right up my alley...once I know why the fuck my brewer won't make more booze for everyone (tip: make sure you have empty barrels, even a single unit of food in them makes them unavailable for storing alcohol, alternatively make more or make glazed stone pots)!
As for complexity and depth? As long as you ignore any metas, there is a massive amount of complexity and depth to it. Fairly realistic biome generation with (now moreso) mostly realistic physics like gravity, temperature, water flow/pressure, seasons, and a wide variety of realistic and fantastical plant life, geologic formations, items, etc mean there's a lot of combinations and interactions. There are a handful of bugs like embarked fruits being unusable for brewing leaving just pump helmet mushrooms for your first booze to suppliment what ale you bring with you until your crops/gatherers get to work. Your dwarves could really go for a bit of an IQ increase and improved attention span, but it's all part of the fun.
Best way to approach DF is to accept that you're going to fail, you're going to fail a LOT, sometimes frustratingly and sometimes hilariously as you watch the carnage caused by a single dwarf having one tantrum too many (rightfully dubbed "Tantrum Spirals" when they lead to the destruction of your fort), and once you at least know what things mean on the UI (looking up the DF Wiki is your biggest friend here, most players encourage it) know that each lost fort learns you about something new or something a bit better in the game. There's also Adventure Mode which is more in line with RPG roguelikes, and you can even find and explore/interact with existing or lost forts from Fortress Mode.
In my opinion, metas take the fun out of EVERYTHING, boiling any game they're made for down to formulaic "use X character with Y moves and Z gear and do A, B, and C to win, everything else makes you inferior" and its why I can't touch many games...
EDIT: Ohey, I actually got the spoiler tags right while drowzy/in bed and getting ready to sleep without using the insert buttons. Go me.