Gentlemen, start your frustration.
Start with the other AI racers and the physics. Basically, there's two distinct laws of what passes for physics in this game: the one the AI racers adhere to, and the one you're stuck with. Watch as the AI vehicles corner with precision, time and time again, as you're stuck having to either brake or slide. Apparently the AI racers also have nitro boost as well, as they can blow past you any time they feel like it, whether you're topped out or not. Oh, there's the finish line in the distance...wait, here comes one racer...now two...now THREE...that's OK, I'll look in my rearview and try to cut them off...wait, I don't have one! Wow, look at that bike that's stuck on the side of a MOUNTAIN suddenly launch itself upward! Ooo, it looks like I'm going to beat this helicopter...wait, suddenly just before I cross the finish line the helicopter blows past me yet again! Sorry, but having to repeat races (especially LONG ones, as many of the events in FUEL are) due to absurdly cheap AI is not at all fun, nor fair.
As for the actual world all of this "fun" takes place in, suffice it to say it's a mixed bag at best. Visually it's not THAT impressive, with textures popping in (and out) all over the place...nothing like losing a race due to hitting debris that popped in a bit late. Give me a POLISHED world half this size, packed with sights that aren't so repetitively dull, and I'll take it over FUEL's barren, uninspired landscape in a heartbeat. The "goodies" you can get for exploring, such as new paint jobs, aren't even close to being worth the time it takes to find them. The fact that FUEL lets you jump into events without doing too much extra driving tells you that Asobo might have known that their "oooooo isn't is BIG" world isn't all it's cracked up to be.
Although you win fuel simply by completing career races and challenges, to give you a little more incentive to roam around, there's several fuel barrels scattered about; hitting them will also bolster your fuel total. Since fuel acts as currency in this game (and as a weak excuse for a plot), you then use it to buy new vehicles. Not only are all the vehicle automatics only, once you buy one you can't change a thing on it except for the paint...you also can't trade it or sell it. Even worse, the game often pigeonholes you into choosing ONE VEHICLE for several of the events. So despite the fact that there's several vehicles to buy and own, the game, in all its infinite wisdom, far too often makes the choice for you. Sadly you'll eventually learn not to make the mistake of going to the garage to buy vehicles on your own, because there's too good a chance that you'll try to open some challenge or career race, only to realize that you didn't buy the ONE SINGLE SOLITARY VEHICLE the game has chosen for that event. Stupid, frustrating, and completely unnecessary.
Yes, there's actually moments where things come together, where you're not cursing something out (expect your fair share of that), but your "restart and endure the load times" moments will far exceed the happy ones. With so many other racers out there that either hit the bullseye or come damned close, it's impossible to recommend FUEL to the masses. Open world racing? Try broken world.