Got mine today and have to say it's a 50/50 thing when compared against the SB800, which is what mine is replacing:
The build quality feels excellent and it has a weight in the had that makes it feel utilitarian and workmanlike. Although it's fresh from the factory, I can see the sureness of the mechanisms remaining so, which is why I like Nikon speedlights.
The swivel head is excellent - 180-degree coverage whichever way you twist it. The angle/swivel adjust button in the head isn't as good as that on the SB800.
I love the clip-on gels and the fact they're so easy to use with the diffuser.
The locking lever on the hotshoe is secure but not as smooth as that on the SB800. This will hopefully free up a little with use.
I don't like the fact you can't just swivel the command dial on the rear to adjust power - you have to press SEL first, which is what you do on Canon units and the reason why Nikon's have always been my choice. Poor decision.
The LCD is much clearer than that on previous flashes I've owned.
I like the sliding mode select on the side - reminiscent of the old SB24/25/26, but easier to use. No stroboscopic mode though as far as I can tell....
Non-recessed optical port might be beneficial.
The batter compartment is a departure and I'm disappointed there's no clip-on 5th battery compartment. I know this is effectively an SB600 successor but I thought Nikon would have seen this as a must, seeing as it's a 'baby' SB900.
No external battery connector - massive flaw. Good job I don't use these at the moment....
I love the big red test button
The menu system is easy to use thank to the OK button and command dial. Easier than the crosshair on the SB800.
The switch that turns the flash on/off is nice, until you decide you want to put it in master or remote mode - you need little girl's fingers to press the button AND turn the lever at one time. Bad design IMO, although I suppose it means it isn't switched over accidentally.
Love the case it comes in - tidy and tiny
I'm sure that with full use I'll find out more things about what looks like a pretty decent flash. I know it's not actually a direct replacement for the SB800 but at the price it's pitched, it's the obvious decision for me. The jury isn't quite out but we'll see.....