The real endgame mechanic is unlocked after you beat the Elite four at lvl 100. It is essentially rebirthing pokemon to relevel and increase IV which is pretty nice for min maxing. Time lock mechanic for areas might not be for everyone but after a week i have farmed most of the pokemon and maxed IVs for those. Raid areas are interesting but currently after T2 raids i have not encountered any harder content. Obviously should be pretty easy to fix and add more legendary pokemon and higher tier raids, only reason i won't give 5 stars. As for strategy i suggest picking one of the T1 raids and farming the same one for IVs during the rotation so you have 1 very strong pokemon to progress with instead of spreading thin with multiple mediocre ones.