I's a very nice lens, one I reach for often. A very good range of abilities.
But steady on - if you're interested particularly in the 1:1 end, and you pixel-peep for resolution and CA, it's only "pretty good".
Quite a few lenses I have, beat it. Some are unfair comparisons because they're bellows-only specialist things, but a small number of the (other-rmakes) macro-to 1:1 lenses do better too.
The point is, that there's scope for improvement. I wouldn't be surprised to see a "II" version come out at double the price, though maybe not a worthwihile improvement for other than geeky stackers..