Overall it's a very good lens and a good investment. It gives fantastic results when used at f/4 and also gives very good and perfectly usable images at f/2.8 It's only a notch off the Nikon and Canon alternatives. I am very pleased with it and have not regretted buying it one bit.
A bit soft at f/2.8
Great Build Quality, Stabilizer works very effectively with low shutter speeds, has a very heavy and solid feel, silent and fast autofocus; It has very smooth zoom and focus rings; It performs great in low light situations and provides high shutter speeds