[Nexus 9 General] :
In fairness, I think there's now a second production run of Nexus 9s out in the wild that have improved a lot of issues (I suspect the OP was referring to AndroidPolice; I have no real qualms about tossing out the name, and they also ran a report on the likelihood of a second run because users were seeing less flex/improved button responses) with the initial hardware. For me, I've not had trouble with light bleeding, and the buttons, while shallow, aren't too problematic. Same deal with the back.

I've paid around ~$400 USD several times now for tablets; a Samsung Galaxy Tab 10.1, the iPad 3, and the iPad Mini Retina. At that price point, I had a certain set of expectations that were-- yes-- gauged against my previous two ~$400 tablets (both iPads). In between, I'd experimented with the two Nexus 7s, but very little can describe how much I truly hate 16:9 on tablets, and they never really found a home with me. I'm trying very hard to like the Nexus 9, and outside of poor standby life, I really have enjoyed the experience so far.

That being said, I've run through a lot of Android devices and a lot of ROMs, and I'll agree with some previous posters-- I'm starting to get a little tired of the "need" to root and flash. It's not that I don't want to, or that I'm not interested, but it only takes a little bit of a hurdle to make other projects vastly more interesting. As has been pointed out, Lollipop changes a fair number of things about Android's internal architecture (the full switchover to ART, for example, which obviously impacted a lot of runtime tools like Xposed, the support for 64-bit architectures, and so on), and many consumer-facing decisions, such as default encryption and system partition checking make it just a little harder to bite into some of what we used to do.

I think the community will come soon enough-- it's a Nexus device, one that like other previous iterations has had a lot of bumps in the road at the start. But it's reasonably powerful (though the chipset seems to still have some trouble keeping the UI thread running smoothly), has a nice screen, and a 4:3 aspect ratio. That combination is likely to bring in more developers once the price falls a bit-- especially in comparison with many previous Nexus devices (though I believe the Nexus 6 forums are more "alive").

On a previous subject, I really don't think comparisons between the Nexus 9 and the iPad Air + variants are unwarranted. At a hardware level, the Nexus 9 has a similar profile to both iPads (both the Air and Nexus 9 are squarely in the "big" tablet arena-- there's a clear distinction between both of them and even the largest of phablets) and similar form factor (in re: aspect ratio and resolution). They're also both running some of the best respective chipsets you can find in mobile. From a software perspective, they're also both running the latest and greatest stock firmware from Google and Apple, and both tackle many obviously similar challenges.

iPads don't work for everyone, but the argument cuts both ways: Nexus devices certainly aren't for everyone either. On Android phones, I generally prefer being able to swap out my launcher because the physical size constraints demand particular types of interaction (I use Action Launcher). On tablets, my preferences flip-- I don't spend a lot of time in the launcher, so the iPad's fixed grids work fine for me on the most part, and most Android tablet launchers just drive me a little crazy.

Despite that, the iPad's gotten very good and solid reviews in all of its iterations. The worst that's been said about it is that it's been too boring, with too little changed. That's not something that I can remember really being said about any of the Nexus devices, which, for better or worse have each made at least a few adventurous decisions. I think sites like AndroidPolice (and others, but I'm guessing you're referring to AP) are doing their due diligence by keeping track of the competition, and by extension, keeping Google and the Android team on their toes.

Even as an Android enthusiast (I've used the Galaxy Nexus, Nexus 4, Nexus 5, HTC One M7, and the iPhone 5S; tablet-side, I've owned a TouchPad, Galaxy Tab 10.1, Transformer TF300T, Thinkpad 10.1, Nexus 7 (2012), Nexus 7 (2013), Nexus 10, Novo 9 Firewire, iPad 3, iPad Mini Retina, Surface RT, and now the Nexus 9 -- so I've tried the whole spectrum from cheap to expensive), I think there are a lot of things about the Nexus 9's release that were obviously sloppy. Some of Google's flagship companion apps (Google+, Hangouts) are embarrassingly bad on a large screen. The device occasionally locks up. The processor heats ludicrously fast (although hardly "burning"), and Lollipop has got some general weirdness to it still.

"But it didn't affect my device!" So what? There are variances in QA for all products. Everyone accepts that. The problem is that those variants can be centered around good or bad points, and at the moment my experiences lead me (and probably others) to believe that iPads are "safer" bets for now. Yes, they don't do as much, and don't try to either-- but when you're engineering software/hardware, less can be more a lot of the time.

Anyway, bottom line, I think we all do ourselves a favor by benchmarking the Nexus 9 not just within the Android ecosystem (where I think will handily beat most of its competitors once the software matures a bit) but to the best and brightest overall, be its competitors from iOS, Windows, or some-yet-unknown corner of the market. I wouldn't lay the blame for the Nexus 9's lower adoption rate to reviews that fairly place it within the overall tablet landscape.