With f/6.3 at the long end, it's not ideal for sports where you may want faster shutter speeds. Focussing isn't the fastest but it can keep up reasonably well once it's locked on. Sharpness isn't fantastic wide open (then again, it never is) but gets a lot better at smaller (f/11 or smaller) apertures, restricting shutter speeds even more. TBH, the price is its biggest asset. The more modern design 150-500 OS version is a bit faster to lock on focus (but still not that quick) and is a lot easier to shoot with handheld (due to the OS) as well as being sharper wide open. The f/6.3 still restricts the shutter speed though unless your body can give great high ISO performance.
For some wildlife shots though, it can turn in some great pictures. Not so good for action shots, as above but for relatively static animals (birds on water or feeders etc) it's hard to beat, especially at the price. Don't forget the tripod though - it's not a light beasty.