Actually, some are really good. I'm a Minolta user, and a complete addict to Minolta glass, so sorry for the comparisons being made with Minolta. Generally, I feel that it's the best (Leica, aside). However, I still concede that I'd much rather the Sigma 12-24mm EX DG than any other wide angle lens from any other manufacturer.
As for macro, I love my Minolta 100mm 2.8, but also, I concede the Tamron 90mm and 180mm perhaps have an edge on the Minolta 100mm (but not sure about the very rare Minolta 200mm macro). I live in Japan, and on Saturday evenings there's a photography show on, sponsored by Canon, and all the photographers on it are professionals who are either Canon users, or obviously aren't. Every time I see one of them use a macro lens, it is without fail, the 180mm Tamron macro (thought the programme doesn't like to say this).
As for primes, I think the Pentax 50mm has an edge on the Minolta 50mm 1.4, but these two are perhaps better than the top Sigma equivalent, though, some will say the Sigma is better. Anyway, based on reviews at DPReview, they suggest not to bother with a 50mm Canon or Nikon.
I can't say much more, as I haven't seen the reviews, haven't used much else. Three good places to check are
PhotoDo,
PhotoZone, and
DPReview.