I don't own one but I might pull a trigger on one of the fire sales. I have played with them a lot in airports (I travel a lot). For speed, focus, responsiveness, performance they are as fast or faster than many DSLRs. They have some very impressive burst speeds, and the continuous autofocus is by far the best of any mirrorless system.
The camera are small and well built, as are the lenses. The performance when attaching Nikon F-mount lenses is very impressive, far better than any other system. Attaching a 70-300mm Nikon VR lens to a Nikon 1 V1 gives about the best wildlife camera you can get for less than the price of a car. In general the smaller sensor works very well for long telephoto
Lenses since they can be much smaller.
IQ is good but behind some of the other mirrorless systems. It is close to older gen DSLRs and is perfectly adaquate for most shooting. If you are printing huge or need to shoot in candle light then you will want a FF DSLR. Also if shallow DOF is your thing then look atthesony FF NEX cameras.
The downsides are the limited lenses, and mostly slowish zooms but the odd prime is very nice. Even the V2 has modest ergonomics with a lack of controllable features through buttons, instead you need to navigate a poorly designed menu. Typically way overpriced but often dirst cheap when previous model is on fire sale. These sor was above average for its size when released but Sony has slightly better sensors now. A new sensor bump would help keep it ahead of the game. Also the accessories can be big and expensive.
It's an incomplete system so far and Nikon are too slow to release new lenses and release a 1 camera with noticible better featuresthan the previous. Makes a lot of sense as a small casual/backup camera for Nikon shooters, otherwise the m43 system is a lot better for people who want a complete CSC setup.