Once it is all said and done I think that generation of Nexus devices was a complete let down, not that the devices are bad by any mean but I don't see how they are giving OEM any direction or hint about where Google would want the market to go.
The Nexus 6:
It brings nothing to the phablet market, specs are high end for sure but that is not enough to set the device apart. The form factor would have been relevant had Google decided to make stylus an integrated part of the Android experience. They did not and as it is the device completely lacks a sense of purpose. Even as a vessel for Lollipop it feels an unnecessary as lots of flagship phones are to receive the Lollipop update soon enough.
More broadly my pov on the topic is that the phone market is crowded enough, competitive and innovative enough, Google does no longer need to push its own devices. Google tried to push its vision of a more unified Android (Android One, Android Silver, Google play editions) and it got rejected by the market actors, manufacturers need to differentiate themselves from one anothers and the bulk of the users don't care either.
What the Nexus line of phones provides can find in Motorola current offer for example, more market actors could also decide to cover than market niche: good support, close to vanilla experience.
Sum Up: a good phablet but it certainly lacks any sense of purpose.
The Nexus 9:
I strongly dislike that one as it is an as unimaginative as can be copy of their main competitor's, Apple, take on tablets too bad Android and all its apps are meant to run on wide screen.
That means a lot of work to adapt existing Apps (and actually for now few incentives for the developers to do so till there are a lot of Android tablets with 4:3 screen ratio).
I do get that 19:10 and 16:9 formats makes for pretty long devices, that it is not the most convenient form factor for reading, browsing web yet it has it upsides. It is great for media consumption, and for gaming for example. It also allow for 2 windows side by side as Samsung and LG custom UI allows for example.
There are many shades of grey, it applies to screen ratio too (and form factors) there are quite a few options between 16:9 and 4:3.
A 3:2 screen ration could have been a good compromise (though I would have stuck to 16/9 myself).
Form factors could have been further altered through bezels and speakers placement in the search for something that "feels" more like a magazine.
Something Google could have been well inspired to copy is Lenovo or MSFT idea to have a proper integrated stand included to the tablet, something that needs to be standardized. A breakthrough could have been a kickstand that allows for both portrait and landscape mode.
It is also failed to catch up with the trend of lighter devices.
On the tech level Nvidia SOC seems to do a good job, though I think lots of reviewers usually so keen on reporting any difference between 432PPI and 486PPI (random figures) did not noticed that actually the Nexus 9 is a step back from its predecessor the nexus 10 and from another 8.9" tablet, the amazon Kindle Fire HDX 8.9". Both managed to provide the high quality printing experience marketed (oops reinvented...) by Apple as "Retina" experience.
Sum up: if the Nexus 6 lacks a sense of purpose and won't drive the market anywhere it is a least a very good phablet, the Nexus 9 actually takes the risk to drive the market where it should not go, triggering a lot of useless work from developers. Its design is passable, going backward on some front, reported built quality is not great.
I do not think that all of sudden the guys at Google turned bad but they might be operating within too much constrains at the time or they need a big shake up and try to have a fresher look at things again.
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Big sum up:
At this point I think that as Google vision for a more "unified" Android failed, their own line of products is now between a rock and a hard place: they are not longer willing to compete on price with manufacturers that support their ecosystem, and it seems that they are also unwilling to integrate features that would nullify some big manufacturers selling points (I think specifically about stylus support and multi windows support, wrt to design integrated stand could also), I could certainly be wrong but from the "outside" (/my pov) it looks a lot like that.
Overall the Nexus line lost its sense of purpose, it was created to drive the market in given directions, it did for phones for tablets though I think the issue is that the line does not have to go on based on legacy (wording).
The Nexus line should be used to push new usages of Google OS and services, it could be a wearable, it could have been an attempt to revive "pod" type of product (a bit like amazon cheap kindle fire HD 6") or trying to reach for the living room as the NExus Player does (imo in a really unsucessful way too).