I use Panasonic micro 4/3 bodies, so for a long time, this lens lacked appear for me, due to the lack of in-body stabilization on the Panasonic cameras. I upgraded to a G9 last year, however, and decided it was time to take the plunge. I bought my copy of this lens used, so I don't have the original folding lens hood, but it's working fine with a knock-off Canon lens hood.
I used to shoot Canon crop bodies, and had the mighty Canon 70-200 f/2.8L IS USM II lens. The Olympus 40-150 f/2.8 feels every bit as serious as the Canon L. Focus is fast, even though the G9 can't take advantage of depth from defocus; the zoom and focus rings are smooth and perfectly dampened, and the lens' construction is solid and reassuring in your hand. Images taken with this lens are sharp, with great color and contrast. Period. Every time. No noticeable defects in the images, sharp across the frame, even wide open.
I have the Panasonic G X Vario 35-100 f/2.8 OIS lens, and there's nothing wrong with that lens - it's also sharp, with good color, and very light weight in comparison. But I find I use the Olympus instead, just because the extra 50mm of zoom makes a big difference in wildlife (plus I have the 1.4X Olympus teleconverter to get even more reach when I need it). I do find the Panasonic lens to be more useful for shooting indoor video - e.g., kids' orchestra concerts - thanks to the slightly wider angle.
Gripes about the Olympus 40-150? Just a few, but not too few to mention. I like the idea of the focus clutch concept to switch from manual to autofocus, but it's left me on more than one occasion trying to figure out why the stupid camera isn't autofocusing. It would be nice if there were a way to disable it for fumble-fingers like me.