MachineClaw
I'm going to be brutally honest.
 
I originally bought Komplete 8 then I upgraded to Komplete 9 ultimate and new Komplete 10 Ultimate.  I have invested.
 
of all the toys and samples and plugins in all of Komplete 10 Kontakt is the only one I use on a regular basis.  I mostly use Kontakt with 3rd party non Native Instruments Kontakt libraries.
 
The drums and basses are good decent samples and you can get by with nothing else for a long time with them.  Battery, Damage, all the 50s & 60s& etc drums, Cuba etc there are a ton of drums in Komplete.
 
I use Ez drummer/SD2 from Toontracks and have most  recently used mostly FXExpanssion Geist and BFD 3.  I don't hardly use any of the Komplete drum stuff anymore, or at all.
 
Orcestral Strings in base Kontakt are okay and decent, there are a few string packs for Kontakt depending on if you get Komplete basic or Ultimate.  Frankly I use 3rd party orchestral libraries for Kontakt like Orchestral Essentials I, Heavyocity libraries and recently mostly being using Vienna Instruments libraries that does not use Kontakt at all.
 
Effects in Komplete are good and if you get Ultimate the ones in Ultimate are much better and quite usable.  I use 3rd party VSTs.
 
Komplete or Komplete Ultimate are really great starting out packages - or if you need Kontakt and or 2-3 other products then it's really worth it as you get a ton of extra fun stuff for the price you would be paying for 1-2 products are full price. 
 
Honestly in a year you probably will not be playing with 75% of the products in Komplete or Ultimate.

Thanks for the full overview.  Very helpful for expectation management.

If I was starting again, knowing what I do now, I would make Komplete my first buy. At the very least I would get Kontakt but it makes more sense to spend a little more to get Komplete. Ultimate is something you can upgrade to if needed, as it always goes at a good upgrade price at least once a year.

Just don't fall into the upgrade trap for each version.

Komplete was $999, then $799, then $699 for only 11 instruments back in the day. How things change! The one good thing to come out of the financial crisis was cheaper plug-ins. Sure, you lost your house, job and everything else but your plug-in folder swelled nicely.

plug off 

Fleer
plug off 

To the Great White North!!!

Hey Hosehead, let me have some of your beer, eh.

Here's my thoughts on it. I upgraded to K10U for a few things. Namely FM8, Damage, Kinetic Metal and I was interested in Rise & Hit though not sure how much I'll use it.
 
As far as the NI libraries themselves, they are very "meh" worthy. The drum kits don't stand up to AD2, the pianos are okay but you can find much better options, same with the guitars, Action Strings/Strikes is insanely overused and easy to spot in things like commercials, the Session plugins are rubbish imo.
 
That said, if you want things like Reaktor, Massive, etc as base synths, then it's well worth the cost. Plus many libraries you can't even use without Kontakt. The presets for their synths are okay. They are a company that makes the tools and hopes that sound designers pick them up and create better sounds for them which is fine. Serum is essentially the same in that aspect. Just expect to spend more money if you're not a sound designer.

Even though I have been with Cakewalk since it came on a floppy! It's only been in the last 2 years that I have started working almost exclusively Out of the Box.  When I upgraded to Platinum early this year I picked up Komplete 10 on sale then upgraded to Ultimate when they had a half price sale as my first big foray into softsynths etc. INHO it was worth the purchase even though there are some things I may only use rarely if ever. Having so many tools to experiment with as I dove into the learning curve alone was worth it for me. And of course the information that the Very gracious people in this forum offer help make the learning process a lot less painful!   

Got Komplete 9 a few years back, and also find myself using mostly Kontakt for obtaining 3rd party samples
(aka more spending)
I don't find the NI synths very useful, because I can find exactly what I need much easier in Omnisphere
(aka more spending)
The kind of music you do will determine how useful all the Komplete extra goodies are for you.
 
For "Ambient, shoegaze, modern post-rock type of stuff" ? you may like the organs, Absynth, FM8, some edgy guitars, great Bass samples . . . and finding that perfect synth patch for your tune in Massive . . . hope you're lucky, and have time on your hands.
 
I'm glad I never spent the extra to get Komplete Ultimate, because there are so many amazing 3rd party sample collections available that work so flawlessly in Kontakt, and in Sonar . . . my money was better spent there I'm sure.

I'd go with Komplete over Ultimate as well.  I have had some version of Komplete since K5.  I haven't had time to learn everything yet.  The included Reaktor ensembles alone could keep you busy for a long time.  There are a lot more in the user library as well.
 
Considering your interests, I think you will really like Absynth, as well as some of the Reaktor ensembles.  The Giant is a good piano for Ambient sounds.  Also, the Arena kit from their Studio Drummer is a good start for post rock sounds.
 
Massive is billed more as an EDM synth, but there are a couple of spacey pads in there.
 
You probably will want to check out some of the Hollow Sun and Hideaway Sounds Kontakt libraries.
 
 
 
 
 
 

Massive is indeed marketed as an EDM synth, but I think it's one of the best multi-purpose subtractive synths out there. It's got wavetable oscillators, filters, feedback loops and a myriad of modulation sources and effects, plus one of the most intuitive and easy to use interfaces for executing your sonic ideas. Doesn't matter what kind of music you're making, if you need straightforward synth sounds then Massive is more than capable. It's also great for those out there EDM sounds too, if that's what floats your boat.