So the issue with mine is...
It came with 5.0.2, and after turning it on, it installed a bunch of updates that eventually got me to 5.1.1. Cool beans. But for some off reason, the tablet would freeze randomly and reboot. I thought maybe something was wrong with the OS, so I tried to restore it to factory settings. Still got random reboots. So I thought I would try to flash back to KitKat. Downloaded the image from Google's list of factory images, but it would never get past the Google screen. I then redownloaded 5.0.2 and that seemed to get it to work. Updated again to 5.1.1. and the tablet ran fine for about a day.
Now today...I left it to charge. About an hour later, I checked the tablet and it was again, stuck on the Google screen. I never turned it off or anything, so I don't know what happened. Every time I turn it off, it would just turn right back on. I tried to go to recover mode, but like the OP, it just hangs on the Google screen, never gets to the Android lying on its back. Tried to turn it off again, nope, keeps on turning on.
Since it wouldn't go back to recovery mode, I left it at the bootloader, and tried to flash 5.0.2 and 5.1.1 using BOTH WUG's Nexus Root Toolkit, and just a regular adb cmd window. There are no errors in the logs, but neither one gets me past the Google screen.
So... on a scale of 1 to 10, how screwed am I?