FWIW, the round is good enough for whole police departments to adopt it. They make the statement that 357 Sig gives them the penetration that the 40 S&W doesn't, ie., car doors, some armored vests, building structure etc. And they still don't have to deal with the recoil of rounds like the 10MM(which I have never had a problem with).
For us civilian types who don't typically need to shoot through car doors or armor, it's not really that much of a big deal.
Performance. It's not that big of an improvement over the 9 mm +p+. I'd wager that .38 Super, done right, could give it a serious run. Then of course there is the .357 magnum, which while down on capacity, still can easily outperform the Sig when bullet weight climbs above 125 gr.
Magazine capacity. All that marginal improvement comes at the expense of magazine capacity.
Cost. Those of us who don't have the taxpayers buying our ammo have to actually consider the value added by this cartridge.
Reliability. I seen it said elsewhere that bottleneck cartridges feed more reliably. My question is: if my current non-bottleneck cartridges feed with 100% reliability, will I still see improvement?
.357 Sig wasn't a huge leap forward. It was a side trip. Even if one agrees that it's an improvement in one way or another, the question then becomes: How much and is it really worth the extra cost?