Pay 2 Win + Unbalanced Matches = Bad Combination (plus mini guide to completing quests)
I have a bone to pick about this game, not specifically because it is a bad game, it is actually quite fun in co-op but the game is set up more for multiplayer than the co-op missions. You only have a certain amount of fuel you can use to play co-op missions, about 5 to 10 a day or more depending on how much fuel you have (if you use a fuel barrel in multiplayer missions you can get 5 or more per match you win but you have to survive and the things explode, so good luck with that). The problem more becomes apparent when you're playing missions for parts after you run out of fuel, which are not heavily restricted to who can join. The game does do a good job at putting pure noobs together at first, but soon it becomes apparent that people who put money in the game or who have been playing it more are going to be in the same bracket as you no matter which mission you choose.
This creates a fairly large imbalance within the game when people with anti air guns or better machine guns and amours, or even rockets and energy weapons can enter you game and play against you with basic machine guns and basic shotguns. By having such a buyers market for the game available it creates huge inconsistency and makes some people into pub smashers while some just want to advance but lose all the time. This becomes apparent when your main form of leveling is the 40,000 reputation bonus you get per day, 20,000-40,000 of that which you'll be able to grind in co-op missions if you are lucky and get good teams. The rest you'll have to do in those unbalanced missions. And if you leave those games, you'll sometimes be put in the same game again or put on the losing team you had last match, which just feels like karma after awhile.
Now as for the leveling in this game, it's based on reputation. That daily bonus I talked about is really your only method of leveling fast at all, so you'll have to come back every day after it resets to get the maximum leveling bonus. When I was playing the game the Bananatic quests were for level 5 reputation, level 8 reputation, and level 13 reputation. So if you don't want to wait for a new quest to show up, you can go by those guidelines, even though they may be random for you (just take a screenshot every level after you're done the first quest or even before that). As for advice in playing the game, it depends on what weapons you're using, so here's a few tips for all the entry-level weapons. If you use machine guns, max out as many as you can use, use a car jack (you don't have to but I find it super useful), and a radiator that lowers your ammo reload. And load them up so they don't hit into each other's firing arc. Shotguns are close range weapons, don't use them as a cannon. With both shotguns and machine guns your main objective should be to shoot off the enemy's weapons so they are defenseless. Cannons should stay back quite a bit and try to be mobile so they can get away if need be since most people use machine guns (there will be cannoneers in nearly every match anyway). Always try to shoot up a bit from where you're aiming if you're far away. Aiming a cannon can be very hard but it generally shoots right in front of it so you'll have to maneuver a lot. Well that's my review and I hope you have fun blowing up cars =D