The game right now is okay for new players since they have 3 complete regions to have a go at, and will soon have Sinnoh to play. However, as far as end-game content goes, it's a bit lackluster other than competitive play and shiny hunting. I've been playing this game for over 7 years now on and off, and the main reason I've quit a few times is simply because I get bored of the same old grinding methods.
For this game to succeed and to carry on going for many more years in the future, they need to consider adding more end-game content such as:
Dungeons for catching legendary and hidden ability Pokemon (I know this is planned eventually, but I think this should have more priority over Sinnoh imo)
More content surrounding teams other than the social aspect, this could be a big one since the main reason people stick around is because of the friends they've made in their team - I'm talking team wars, team missions, team rewards etc.
More drive in the other tiers with regards to matchmaking - Something needs to be put in place that gives more opportunity for UU and NU to shine in matchmaking (and maybe even LC and doubles). Doing OU over and over again gets tedious when you don't mix it up a bit
Some kind of achievement system that gives you rewards based on certain actions (e.g. catch this pokemon in this amount of time, walk this many steps etc.)
P.S. bring back Off Topic and Round Table pls