Crimes detected are random open world events & they involve usually stopping a crime in progress by taking down the criminal, these can be extra difficult if the public contact the police.
I've not done any criminal convoys or fixer contract missions yet (apart from the campaign missions) because I'm waiting to unlock all of the skills to help me complete these side missions.
You also have Investigations icons on the map these mainly use your hacking skills & once you have completed a particular investigation it will result in a final mission for you to take down a criminal. I've completed the Human Trafficking, Missing Persons, Burner Phones & Weapons Trade investigations leaving QR Codes to yet complete.
If the above was not enough you have a bunch of collectibles from audio logs, song sneaks, privacy invasions to cTOS Breaches.
The game has received some negative press mainly due to the graphics downgrade from the E3 reveal The gameplay (driving excluded) is very good, I'm enjoying hacking & using stealth in combat to take out enemies.