I traded a few manual focus lenses that I hadn't used for this Tamron SP 90mm f2.8. I used (and still have a broken one) one of the first version of Adaptall 90mm f2.5 briefly, also a fine lens, but the modern AF version is simply much better. Extremely sharp, even at f2.8, and even at infinity, which the lens was not optimized for. No, it's not as good as the Canon 100mm f2.8L IS. The sharpness of that lens is legendary, but the Tamron holds its own quite well, especially at less than half the price of the Canon. True, the 100mm f2.8 has image stabilization, and is much better built.
One of the things I don't like about his lens is the focusing. It's nothing like the EF 100mm f2.8L with its UltraSonic Motor (USM) for lightning fast and silent focus. The Tamron is a lot noisier, slower, and less accurate. Once in a while, I would get a picture not critically focused. Not ruling out user error, though.
I think this lens is an excellent value, offering versatility from macro to portraiture, and 90mm is a very comfortable focal length for full frame as a short telephoto. In fact, I am quite impressed by its image quality. If you overlook its plastic construction, occasional mis-focus (or user error, not sure), it's a great value.
All pictures below were taken with the Tamron SP 90mm f2.8 and Canon 5D Mark II.