I think this one asks you to pay for it after a bit. Not that there's anything wrong with that. Just felt bad about getting a little bit in, and then being hit with a decent pay wall.
Personally, I would happily pay for vim-adventures, but never monthly. It provides one-time value, it should have one-time cost. I'd much rather pay a one-time cost and get a downloadable local copy.
Right, I mean, author has the right to do this -- but it still seems like a gloriously stupid thing to try to get someone to pay for in this way; like what market is this?
Like, I'd bet "Pay $10 if you like it" / ReaperWare would earn this person literally an order of magnitude more money.
I paid for it, was worth it for me. Reason: I did vimtutor 4 times and was learning but found it super painful/boring, but really wanted to learn vim keybindings. Vim adventures made learning keybindings and muscle memory just tolerable that I could do 1h in the evening even after a long/busy/tedious day. I probably would have persisted learning vim keybindings without it, but it definitely made doing so less painful.
A free alternative for learning just hjkl, nethack supports this way of moving[1]. Remember to keep your index finger on ‘j’ (don’t shift your hand to ‘h’), to build the muscle memory.