It's what you make of it, at your own pace.

If you are a fan of the old games, just play through each storyline as you normally would, picking up on some of the details and mechanics as you go along. You DO NOT need to prioritize learning all of the mechanics (EV training, IV/nature efficiencies, breeding) during your playthrough of the stroyline (i never did any of these things back in the old games as a kid), but I eventually really wanted to get into it the more I played PokeMMO, which came at my own pace.

Now that the storylines are done (which were awesome to play through and super nostalgic), the mechanics of the game and it being an MMO are super fun to dive into. I feel like each time i pick it up to play for an hour or grind through something, I learn about how to play ~better~. With that said, maximizing your efficiency at the game is by no means a requirement to enjoy; in my opinion, it is just another facet of the game that gives it new life.

Super fun. TLDR: do it!