This is eye of the beholder stuff, personally I like to go for more realism, however, if you don't care that it's got no suspension and cannot steer then I suppose it's fine. I would however go for a few hundred more triangles though. You've got more triangles in one wheel than in the enitre body of the car which to me seems a little odd.
Only after looking at this thread did I look at monster trucks at all really, and it seems that your truck is a truck on stilts whereas actual monster trucks don't really do that.
The tread on the wheels reverses at the top, I assume this also happens at the bottom of the wheel too.
The shape of the vehicle is a little strange too, I'm assuming you've not used any reference material to come up with the design. I would strongly recomend finding reference material and working out what the side view outline of a monster truck looks like, likewise the front and top.
Look at the detail of how they are put together and how they work. Where all the drive shafts are etc, how the suspension hangs together.
That all said, if you're going for a non-steering monster postman pat van truck then you've gone a great job.
