I've used this lens and its predecessor extensively and I've been happy with both. They are clear, accurate, and focused. You can find a zillion reviews talking about how awesome this lens. I'm going to highlight the lens' shortcomings. This is not a be all, end all lens. Don't get me wrong, this is my walkaround lens and it stays on my camera 75% of the time. But it's important to know what this lens won't do.
1. Low light. This is a problem that plagues any reasonably priced long-range zoom. If you're going to be doing much shooting indoors, at night, or twilight with this lens, invest in a good quality flash.
2. Bokeh. The majority of the out-of-focus fields look great. However, if you're shooting wide open (low f stop) and there's a lot going on in the background (long grass, trees, etc) some of the finer details can be blurred or occasionally have a weird halo look to them. It's not that big of an issue, but it does happen from time to time.
3. Distortion. Very manageable and hardly noticeable for the most part, but when you shoot things that are obviously supposed to be very straight (buildings, roads, etc)at less than about 50mm there is some pincushioning. This is easily correctable in photoshop.
4. Light falloff. In low-light and long-exposure pictures, you can clearly see some falloff in the corners. Again, hardly a big deal for most photography.
5. Weight. If you're not used to big lenses, this will take some getting used to, especially if you're upgrading from a kit lens.
6. Filters. The 72mm size is getting more popular, but there still aren't nearly as many filters available as some other sizes. There are resizing rings to compensate if you already have some larger rings, or are eyeballing something in particular.
Ok, this was not meant to turn you off of this lens, only to give you a grounded sense of what this lens has to offer. It is a great walkaround lens for everyday use. It is also a great lens for people looking to get their foot in the door with high quality lenses without having spend too much. This won't replace prime lenses, fast lenses, and superzooms. This is a perfect lens to buy if can only afford, or only want one lens. I would still hate to be without this lens. Highly recommended.