Anyone played Dota 2? Just started playing it and it's one of the most complicated games I've ever played. It superficially resembles your average multiplayer where you play 5v5 to invade the enemies base and destroy their ancient. But unlike other multiplayer games you don't just fight with what you have, you have to kill landscape mobs to make money to buy items, then craft them into more items and gain XP to level up and unlock/upgrade skills in order to stand a chance.
There are 110 characters, each with a surprisingly unique set of skills so it will take an insanely long time to even vaguely know what to do when faced with a specific enemy, let alone the combinations that you face.
You can practice with bots though so you don't have to face real people. I hear the community is the absolute worst, if you're even vaguely bad you'll receive a torrent of abuse for it so I've been happily playing with bots against bots and I'm not sure I'll dare to do it with others.
It's also f2p which is great. It has a business like Team Fortress 2 where the shop exists to sell cosmetic items that have no bearing on gameplay so you never have to worry about spending money on it unless you really want to :D