No, it's not just you. They do get harder, I just wish that they made it so the game has difficulty settings (easy, medium, and hard) so then you can play it the way you want to. I'm not a fan of hard games; I'd rather play a game on easy than hard any day.
I'm a little over 66% done and just over 9 hours into the game. I unlocked all garages and 79 cars, it's a great game, but I find myself screaming and wanting to throw my controller through the TV too much now. The most recent missions I do not like is the one race to get your team in 1st and 2nd. It was to unlock the Dodge Viper (one of my favorite cars) it took me at least 6 tries, with all of them ending with a 1st and 3rd for my team, so I had to quit and play other missions to get enough WP to unlock the Ford GT 40 (100,000 WP). Then it took me another 3 tries to finally beat it. The other ones are the final 3 challenges with the school bus (stay above 70 and get to the location in a certain amount of time), Shelby (get your heart rate to 180), and finally get a certain amount of cars to the cops. I almost had it on the first try but got confused on where to turn and lost a lot of time then got boxed in by enemy cars, so I quit and drove around.
If it wasn't for all the times I found myself screaming at the TV this would have easily been a 10 out of 10. I just wish when people make a game that they have difficulty settings, and not just make the game harder towards the end.