I really like Cities Skylines, however the faulty vehicle AI and traffic in general will destroy the whole town once you reach a certain point of progression and I feel like it makes the game unplayable since I know that I won't successfully make a great big city.

For Example, when making a round-about that is two lanes wide, then as cars drive through it they just clutter the closest lane to the exits; thus leaving the far lane completely empty as immense traffic ensues in one lane.