I must state ahead of time that I'm not a fan of the official Sony PS3 controller as I find it to be too light in my hands. I'm always on the lookout for a second controller that feels right. This Logitech controller is a mixed bag of good and bad. First, the good. The controller is a little heavier than the standard pad, and feels really good in your hands. I wouldn't go as far as to say that it's more solid, but it's definitely heavier and the ergonomics are nice. The analog sticks are far superior to the standard pad, as they don't give as easily. Aside from this, however, the cons war outweigh the pros. The D-Pad feels extremely loose and has an audible click with every press, which is never a good sign for a controller. The face buttons are alright, but the shoulder buttons are just off. L1 & R1 feel very loose and also click, but L2 & R2 don't give enough -- you really have to force them down to get the full range of the triggers. When it comes to intangibles, this controller does not feature any motion sensitivity or force feedback. It does have a feature that allows you to switch the function of the D-Pad with the left analog stick, but it doesn't translate as well as I would have hoped. All in all, this is a decent second controller for your PS3. Highly recommended for shooter fans because of the analog sticks, but everyone else should be cautious. The D-Pad is unforgivable.
EDIT: After spending a bit more time with this controller, I'm starting to like it more and more. The added weight really is a huge advantage, and the triggers are awesome once you get used to them. I'm still not a fan of the D-pad, but luckily 95% of the games out there mainly use the analog sticks. If the PS3's stock controller isn't your cup of tea, I would definitely recommend this to just about anyone.