I lived in Denver for nearly 7 years and loved it. Back then they didn't use salt on the roads, so the cars hardly rusted at all. The sun in the summer can be strong, and folks are lazy with waxing their cars--- so paint fade is common. They also have less octane in their gas--- something to do with the altitude, or environmental issues, as Denver had horrible smog problems into the 90s. (might still)
A slower car can be frustrating heading up into the mountains, but coming down is still fun! (provided you have good brakes, if not....it can be terrifying!) Yes, your car will be noticeably slower. Everything is slower though, so you kind of get used to it. When you head back to sea level your car will feel FAST! I remember my 87 Cressida was a dog at altitude, but at Sea Level it could chirp the tires under the right circumstances.
What drove me out of CO? Life changes, a lack of water, and high cost of living. Denver is basically a high desert, so nearly all lakes / ponds are man-made reservoirs. The streams are nice, and decent for trout fishing, but overall, it's a very dry place. Stock up on skin lotion, and chapstick--- especially in Winter. When I first lived there, the cost of living wasn't bad, but they then had a boom, and prices doubled within 6 months or so.
Keep in mind Denver has always been a "boom town". In the 80's it was oil, then in the 90's it was tech. When these industries explode, costs go up......way up. When a 1,000 sq ft place in a decent (but not opulent) area was closing in on $300K, I left for more bang for the buck.
I have friends that live in Aurora. It's a pretty unremarkable suburban part of town. The cost of living was always lower in Aurora--- probably because it's not really near anything but homes and strip malls. Downtown Denver is only 20 min away though.
Traffic does suck.....badly, but they have expanded the Light Rail, so it's actually useful now. They also have those funky rental bikes everywhere---- but they aren't optimal for the Winter. That said, you plan around rush hour when you live in the Denver metro area. Just don't bother trying to get anywhere from 3-6pm. If you do, surface streets can help once you know your way around. Still sucks though.
I found Denver itself to be an Ok, but not a great city. The magic of Denver is it's proximity to the mountains. Denver isn't actually in the mountains, it's at the base of the Rockies. Depending on where you live in the city, you can get to the mountains in 20-60 minutes. It's very, very nice up there----- God's country!