Mostly the really lame boring ass missions. Heists are really fun and easily the highlight of the game but they're rare and theres way more lame "drive from point A to point B, watch a lame cutscene, drive to point C, watch another stupid cutscene or maybe get in a race/chase/shootout if you're lucky" missions. And then lots of even lamer ones like the tow truck missions, weed alien shooting missions, and forced stealth missions. Shooting is better than past games and the weapon selection is good but its held back by lame cover shooter mechanics. The characters and story have moments but on the whole are completely uninteresting, especially Michael's arc. The online is a TERRIBLE grindfest.
Basically if the whole game or even 50-70% of the game focused on heists, which are cool and fun, it would be decent. But instead the game is as usual packed with stupid shitty side missions and minigames instead.
