Did you get a dodgy sample? The only issue I found was the noisy AF but other than that it was sharper than my then 50mm 1.8 at f2.8 and f4, it got seriously close to subjects and resolved serious detail, even though it had no USM class AF motors or IF it did focus fast.
It was also cheap!
I've had two now, and they've been the same. Maybe the Tamron gods hate me! It is decently sharp in the centre, I just don't find the colours or contrast very good. My old Canon 24-70 I would hardly have to do much PP, the Tamron I have to tweak every shot.