"Fantastic build and image quality, fast IS, but costly"4.5 starson by Shankland
Pros: Image quality is superb. Also: fast focusing, rugged, good image stabilization, weatherproof.
Cons: Worst is cost--try rationalizing it as $110/year for a decade. Everybody wants a wider aperture. It's bulky if you'll always just use cameras with APS-C sensors. $115 tripod lens collar is overpriced. Not telephoto enough for shots of distant birds.
Summary: Expensive, but it has great image quality, build quality, durability, image stabilization, weatherproofing. I've used this lens for more than two years, including many backpacking trips, and I love it. It's also good for photojournalism, even without f2.8 aperture, if you can shoot at high ISO. It's rugged, seemingly immune to very dusty conditions, and modestly hefty. The f4 aperture could be wider, but for me it's worth it to have the cost and weight savings over Canon's f2.8 model with the same 70-200mm zoom range. Included lens hood is nice. The IS is good enough to let me take many photos at 1/10 sec even all the way at 200mm (no, not all come out, but enough do). Would be five stars out of five if the price were a bit lower.