In my books a good game is fun to play.
Missions are mainly shooting and driving... it's the same thing in every sandbox game. But in this you can complete the missions in any way you want. There aren't really any restrictions that make you fail if you decide to do things differently. Which makes the game pretty easy but I don't mind, I just love the freedom. There are literally tons of small side quests out there as well. You can be a bodyguard, commit an insurance fraud, go streaking and do various other things of that nature.
I also like the sounds of crashes, explosions and guns. They were lo-fi but damn did the sounds kick you in the gut. And sometimes you could hear the radio commenting your progression which is always nice.
In the Sims part of the game you can dress-up, tattoo or bling character pretty much any way you want. And you can watch the cutscenes again with different outfits that will change the mood of those scenes completely - I recommend to try it. If you're into laughing that is. This nice feature helps in a way that you don't have to replay the whole game just to see that one certain scene again. Naturally you can also pimp your vehicles and let your inner idiot loose in the designing process.
A nice feature around the combat is that the character tends to automatically reload the guns while not in combat, something I usually forget to do. What can I say about the action. Well, it works like a charm. Weapons are effective and ammo is plentiful. Companions in combat are there but they do not make you stress out because you can always revive them within a time limit.
So if you're into sandbox games and want something absolutely ridiculous. Look no further.