There was another topic here a while back with much the same question;
My objectives are/were;
A) to get to TL40 (done)
B) complete the available dex via actual travel to see parts of the world I haven’t seen (still need Heracross, Tauros, Relicanth, Torkoal & Plusle I think - still have to evolve some Gen IIIs though: Lotad, Trapinch, Wilmer & Feebas lines )
C) at some point get all the Unowns (only 5 so far)
D) max out all of my 100% mons (stardust events are handy but with the list expanding it is now becoming a drain on my stardust resources so this is now becoming a longer term goal…)
E) catch some shiny mons (got 13 so far including a shiny Pichu, Mawile, Duskull & Gyarados)
Now we can add getting to 50m XP - this one is bit of a longer term goal…