I've had my 16Gig GNex10 since Christmas, and had previously a Samsung Galaxy Tab 10.1.
As mentioned, no built in expandable memory, via mSD card, is somewhat limiting. Having a cloud environment helps this limitation, in terms of being able to access music, videos, pics. I have a networked external WD Drive (MyDrive) that serves as a personal cloud and provides me access to my media anywhere I have a wireless connection.
Some screen bleed is noticable, but only when the entire screen is black (during boot-up).
Despite having stereo front facing speakers, their performance is somewhat lackluster. I find myself hooking up my bluetooth headphones when listening to music while cooking because the speakers don't get very loud. My S4's tiny single speaker seems louder than what I'm able to get out of my GNex 10.
Lack of official accessories. No dock, no pogo charger, and the cover that snaps into the back of the tablet only covers the screen & does not fold up as a stand (like other smart covers)
No Miracast support. Miracast is a wireless mirroring technology (similar to Apple's AirPlay) that is being standardized by the WiFi alliance. The GNex 10 was originally advertised as being Miracast compatible, but was removed shortly after release. My understanding is that the wireless adapter tech in the GNex 10 doesn't have the dual band capabilities needed for Miracast.
Raw Google Android experience. In my opinion, this is both a strength & weakness of Nexus devices (particularly Samsungs). On the good side, you are first in line to get Android updates. You don't have to wait on the hardware manufactures to get their custom user interface working with the new version of Android before pushing to the users (which can happen a full year after release).....IF you even get it.
On the bad side, (again particularly with Samsungs) the hardware manufactures have gotten pretty good at mod'ing Android and are able to deliver some pretty cool features & tech that just aren't present with vanillia Android. Samsung's TouchWiz overlay is probably closer to the look & feel of vanilla android than others, like HTC's Sence & Motorola's Blur....but enhance a lot of Android capabilities...and then some.
As for Rooting....it's essentially hacking the OS to give you a higher level of privlidges that aren't available to users. Rooting your Android device is usually more beneficial for non Nexus devices because of all the extra protections put in place by the hardware manufacture & your cell carrier. It allows you to remove software from the manufacture & carrier that you normally can't remove, and also gives you the ability to strip away the manufacture custom user interface and go with a more stock Android experience.
Since Nexus devices already come with a stock Android experience (especially for non carrier tablets), there isn't as much to gain from doing it. You an also "brick" (damage beyond repair) your device if you don't follow the steps correctly.
Last suggestion.....wait around a little longer if you can. Google is set to release the next batch of Nexus devices soon. They've already confirmed the new Nexus 7" from Asus, and there are rumors that the Nexus 11 is on the way (likely later this Fall, in time for the holiday season).
Hope this helps!