How Long Did it Take to Understand This Game?

Your question presumes we understand the game. Einstein once said something to the effect of "The greatest barrier to understanding something is the presumption that you already do."

I know for a fact there's much about this game I don't understand. Maybe that's why I still enjoy it.

No one truly understands this game, even the Balance Team is flabbergasted!

GGG have been making the game for like 7 years and they yet to understand it

It took me a few days to understand the basic trappings of the game, but it took about a month to fully understand some of the more fiddly bits (it was a pain in the ass to find a proper explanation of "increased/reduced" vs "more/less").

I learned most of said fiddly bits with a combination of wikidiving and watching the big streamers/yotubers (projectpt, itsyoji, zizaran, ziggyd, mathil, etc), as well as examining successful builds and trying them out to find why they worked as well as how.

I'm sure there's still more to learn as I go, since I still haven't really gotten to teh crazy endgame stuff yet (through a combination of stubborn atlas, janky personal builds, and cost requirements on gear upgrades)

It took me a couple years to get to a good level of understanding about the game, although there are still plenty of things I'm still learning (that's what keeps it all interesting). There are a couple pieces of advice I'd offer for improving knowledge of the game. Joining a guild with active and knowledgeable players was one of the most helpful things for me- listening to some of the conversions in guild chat clued me in on concepts I wasn't even aware of. Second, don't try to learn everything at once- focus in on one or two things at a time and learn those things well, then move on to the next things. When it comes to things like skills and build mechanics, I'd say you really need hands on experience to learn it will- as in a few weeks to a month actually playing the build from lvl 1 to 90+. Doing that gives a really good handle on both the skill the build is using as well as the key mechanics behind the build (and these mechanics often overlap with the mechanics of other builds, so the process becomes quicker the more times you go through it).

For other elements of the game, it's ultimately just a matter of immersing yourself for a while. You asked about figuring out how to identify good items/how to value items, and for this I'd recommend getting into crafting (nothing fancy- just alt-regal crafting on jewelry). Getting into that will force you to learn prefixes and suffixes pretty fast, along with what mods complement each other. Once you get a handle on that (along with what affixes various builds are after) moving to pricing rare drops is just a matter of applying the same principles to slightly more complex items. Same general concepts of immersion applies to other elements of the game- Atziri, the lab, maintaining a map pool, etc. Pick one that interests you, immerse yourself for a while, ask people about elements you don't understand, and after a while you'll be the one answering other people's questions on the matter.

I started to sink a lot of time into this game back in ambush. I think i grasped the basics quite fast (increased/reduced vs more/less, how can i get damage mitigation?, how do i path efficiently through the tree? etc.) - but i learn new details with every build i play.

A lot of people might tell you, that in order to get started you should just copypasta a build (with the newbiefriendly-tag) and slowly improve your knowledge, but for me that would have killed all the fun. The passive tree was, what got me hooked in the first place, and the learning and theorycrafting process always have kept me interested in the game.

I joined guilds; found the smartest players and learnt from them by asking a multitude of questions BUT only after I had researched and tried first. If i failed, i went to the people for help- never global- waste of time.

and POE, for me, is my first computer game outside of racing games ive ever played. i was pure noob; like, the purest. im still learning some things to this day too!! maths calculations are currently on my need to know list.

i did start playing over 3 years ago when half of the stuff in the game now, did not even exist which was awesome cause i didn't have a ton of things to figure out.

stash tabs have saved m life. most recently, currency tab. if you wanna trade, these are essential!

Been playing since closed beta and I still don't understand Path of Exile. :P