It'll probably just be mediocre. Google needs to get the phones in stores so non-tech people will pick it up. And they need to stop rebranding all their products every year. The "nexus" was a great name for hardware to go along side the "android" software name.
Did you like take it into a store and an employee switched sim cards? I really doubt she accidentally took it out and switched it.
I got that error once and it went away and never came back. Another possibility is you just need a new sim card.