There are few software packages that are as much value as Komplete - look at the price of the 11 instruments that make up this package and add up the prices, you get them for less than half price buying them this way.
Probably the biggest downside to this is how long it takes to install them all and their libraries, but when you see and hear the results it's all worthwhile.
The interfaces have obviously had a lot of effort put into them to make them either look like the instrument they are emulating, or have had a great interface designed for non-emulated instruments. My only criticism here is that sometimes not enough thought was put into how much screen real estate will be taken up by these apps.
I can't really think of anything to say in terms of criticizing the sounds - they all sound great, whether you're looking for digital, analog, high quality or lo-fi.
Documentation isn't lacking either - not only do you get a collection of printed manuals, there is plenty of other information in PDF files that are installed with each instrument.
There are presets galore, with a lot of thought having gone into them. Descriptions of the presets are great too - you get some idea of what they will sound like - something that doesn't always happen with other instruments.
Customer support from NI tends to be a little slow. I haven't really had any need for it with Komplete, but my experience is that you have to be patient with them.
Value for money? Hell yeah! These things work out at less than $100 each and you're getting incredibly high quality for that price!
I've had no problems with stability with any of these. If anything, the versions included in Komplete 5 run leaner than demos of previous versions. NI seems to have done a lot to get these things working as well as they can.
Overall I would recommend this package to anyone. I know it's pricey, but if you have the money you really should invest in this.