Super competent first try from Samsung

Picture Quality:
Terrific frankly, nice clean shots up to ISO800 suitable for your big enlargements, a little bit noisier at 1600 but still fine for 8x10s or more, 3200 maybe for emergencies only - there's a NR function you can switch on that kicks in at 3200, but if you want to get technical best thing apparantly is to shoot in RAW at 1600 and above and process to your own NR taste rather than relying on the jpeg output. I'm referencing the 18-55mm kit lens - If you use the bright & fast 30mm 2.0 lens you're less likely to stray up beyond 800 anyway. From review sites around the net it seems that the overall IQ comfortably matches entry-level DSLRs, and has a more controlled dynamic range (shadow detail, highlight clipping) than it's smaller-sensored 4/3s competitors. I'm using the 18-55 and 50-200 kit lenses, both well built (latter is metal mount) and good-to-excellent sharpness/IQ, especially for their price (I did get the 50-200 on sale for £70!).

Build Quality
Excellent - professional reviews across the web liken it to mid-range DSLRs. High quality plastics, good solid feel to it all, buttons a little mushy but nothing's cheap. Hinged doors to battery, AV connections and SDcard slot all decent. Having handled all direct competitors, this feels the most solid.

Handling
Ergonomics of a shrunken dslr - comfortably works with left hand cupping the body and lens, right hand curled round the handle, with right thumb controlling main function buttons. Great AMOLED screen, pretty intuitive main and function menues. Having the electronic view finder (evf) and flash built in also makes it a more flexible user experience, and better value - No need to attach or pay extra for a flash (a la Samsung's own NX100) or a evf (a la Olympus).

Ease of Use
It's more of a shrunk down dslr, rather than an upsized compact, so for a dslr user it's a doddle to get familiar with the controls and functions, less so for those trading up from a compact - I think that the Sony and Olympus rivals designed their models with compact users in mind - Samsung with the NX10(and Panasonic w the G series) have designed with DSLR users in mind. It also lacks those easy-use and fun features you get with some other models - No easy-guide "Background defocus", "Action blur" etc modes with adjustable toggles, no fun picture modes like miniaturization, vignetting etc.

Accessories:
Small but growing range of lenses, five more coming out in 2011 - Not as extensive a range as some of the competition right now, and the smaller 20-50mm is just a duplicate version of the 18-55mm, gains i-function but loses OIS. Overall the range of lenses available are better value than the competitors - When shortlisting what mirrorless models you're considering, also check out how much the lenses etc are - you might be shocked by what some of the other makes are asking for their different lenses, flashes, straps and even cases!

Problems:

OIS seems to be a poor cousin of its competitors - it's ok but not fantastic;
Odd that Samsung can happily fit OIS into a compact camera's lens, but "It'd be too bulky" to fit into a pancake or even some of the larger lenses - the 20-50 lens would be so proportionally right w the NX10 but no OIS! Almost wish they'd gone down the Olympus route and built it into the body;
Size of OIS lenses - 18-55 is almost normal size, and the 50-200 is like a coke-can - A shame given the diminutive size of the body.