Pros: Excellent durability, very good handling, low noise, good wet handling
Cons: Overpriced, there are better choices, poor snow traction
The Michelin X-One is more than twice as expensive as my point of reference the Kumho Ecsta 716 HP4 (in 205/60R15 size). In addition to being twice as expensive, the X-One is T-rated (up to 118 mph), whereas the HP4 is H-rated (up to 130 mph).
What you get for the higher price is better durability. The X-One has 80,000-mile warranty vs. HP4s 50,000-mile one. The X-One tire seems to not wear much and, I am sure, can last (depending on your driving style) up to the promised 80K miles and possibly more.
The HP4 seems to handle a little better than the X-One, but if you live in a region with snowy winters, get ready to spring for winter tires (X-One does not handle snow well). The handling in wet and dry conditions as well as stopping distances are quite good.
Comparing with (albeit narrower) 195/65HR15 Goodyear Eagle LS, the tires produce much better traction (especially in wet conditions), less tire noise on the freeway and less tire squeal in turns.
The X-One produces not much noise and ride comfort is very good. I am referring to 205/60 tire size; lower aspect ratio tires may produce worse results in this respect.
If you plan on going over 118 mph, the X-One is not a tire for you. I never planned on going over 110 mph, but had several 120+ mph experiences over the last year. Thus, X-One would not be suitable.
The durability of the X-One is a major plus, combined with its handling, ride and noise characteristics. However, I feel that it is overpriced. For some reason, you have to pay much more than Kumho HP4 tire with no benefit in handling, noise or ride.
I truly believe that the 60% durability improvement does not justify 100% increase in price. On the other hand, the X-One is much better than the Goodyear Eagle LS I had before and does not cost much more. The X-One is a good durable tire. If money is of no concern, I highly recommend it. Otherwise, the HP4 is much better choice.