No issues with "smear", shallow/narrow soundstage, or with the high end?
Focus and detail retrieval is as good or better than any I've heard. The only amp with a better soundstage I've heard is the 10 WPC Shindo Cortese.
Those who have heard the NC400 in my system agree on those points. These areas, plus the bass control, are the strong points of the amp, IMO.
The high end is the only area that I think may be problematical for some. Cymbals, etc. are very clean and well defined, with very nice, smooth "tails", but have less subjective weight than other amps. If a speaker has been designed around other amps that have more energy on top, the NC400 may seem recessed on top.
With my RAAL tweeters the highs are very clean, clear and well balanced, but those who like more bite on the top end might not find this aspect to their liking.
Initially my new amp was a bit too forward on the upper mids, but that has subsided pretty notably.
Net, I'm delighted with the sound. It is closer to an "invisible" amp than anything I'd care to pay for. My modded PS Audio GCC-500 (Icepower) amp, which I loved, sounded a bit muffled by comparison, so for me the NC400 is a real step forward at the price point. YMMV.