I find EQ1 has a "hilly" learning curve. It's hard to get started on a brand new account with 0 plat, especially on a freshly launched TLP server. You're thrown in an initially unintuitive UI, lots of windows overlapping other windows/etc, and a deeply complex game. Then once you have the patience to overcome that then it becomes what I consider an easy to learn hard to master sort of game.
I'll pick some examples of easy to learn vs hard to master, from a TLP classic/kunark/velious/PoP under level 55 perspective:
Enchanter class is a great example. Easy to learn - oh, I just have to charm a pet, pass out crack(clarity/KEI/etc), and can go afk in a group?
Hard to master: Same enchanter realizing that class has so much more potential.... For instance under level 55 with spell haste - Whirl Till You Hurl can perma stun one enemy, keep another enemy mezed, keep third enemy charmed, realizes charm is a lot more useful with a tash, realizes tash helps the druid/SK's snare land on red con mobs, and now they're a force multiplier allowing the group to take on red cons and get 7.5% xp per kill instead of the 1-2% kill they were getting from whites/yellows, everyone gets 10 levels for the session and is celebrating.
Now think of the easy enchanter just spamming charm to get control of their mob, vs the one that tash + stun + then charms. Huge world of difference.
Then speaking of charm kiting, there's the skill level of breaking charm and having to nuke 3-4 mobs down, to timing it just right where both mobs have 1 hp left and your first level aoe nuke takes both out - being much more mana efficient.
Same can be said for Clerics, etc. Oh just spam heals? Vs a cleric breaking out the stuns, etc. Same with druids and adding on damage shields + ac debuffs + nukes, etc.
I'd say it goes for just about every class, even bards.