Android Lollipop couldn’t ask for a better showcase than the Nexus 6. I do wish that the software did a better job helping me manage a device this large, but the fundamental improvements to the already excellent notification system have made me more productive already. Assuming Google can work out these first-release bugs, Lollipop itself could be fast enough and pretty enough to spur Android developers to finally pay more attention to design in their apps.
Whether the Nexus 6 will be more than a showcase is an open question. Nexus phones always seem to have some sort of weird sales strategy that limits their adoption. The last couple of phones have been incredibly inexpensive, but lacked carrier support. The Nexus 6 flips that script: it has the support of the big carriers in the US, but it’s no longer a cheap phone at $649 off contract. So the story of the Nexus may remain unchanged: popular with enthusiasts, but a curiosity for everybody else.
If nothing else, that carrier support means that you can check out the size for yourself in a store. If you do, don’t be shy about really hanging out with the Nexus 6 for as long as possible. Using the Nexus 6 is absolutely awkward until, strangely, it's not. When I show this phablet to people, I get the same glassy-eyed "I don’t need this" look that I used to get when I showed them my big, honking pre-iPhone smartphone all those years ago. They all converted. You just might do the same.