It made every bump an environmental hazard. I liked it. Getting that in-flight rotation just right was awesome.
There's a fine line between an enjoyable challenge and tiresome chore. This generally has to do with the what the frequency, intricacy, and reward of the challenge is. Driving in Mass Effect 1 is a very poor challenge because the hazards are frequent to the point of annoying repetition, are a relatively simple hurdle that doesn't require use of any interesting tactics, and the reward is, at most, the satisfaction that your vehicle didn't spin out and ruin your ride.
Ultimately, it comes down to poor controls; this vehicle has no business driving as badly as it does. When I drive my own car, I'm steering a machine; it works exactly as I'd expect and just feels right. The Mako fights my control like a poorly tamed animal, veering despite my control. I imagine you get a similar feeling when a game doesn't let you roleplay.
Why would an uncharted world necessarily have terrain suitable for wheels?
Then why are we sending in a wheeled vehicle at all? Why not a hovercraft like the Hammerhead? Or a Kodiak.
Realistically, it doesn't make any sense to send in a vehicle with poor handling to a potentially dangerous locale with incredibly inconsistent terrain, and it certainly doesn't do any favors for the gameplay.
Remember the BDtS expansion. The terrain there was supposed to be easier to drive, but as a result it was boring, and it was less believable.
That just proves that the Mako was an unresponsive vehicle that wasn't fun to drive at all. If your vehicle isn't fun to drive on relatively consistent terrain, then your vehicle isn't fun to drive.