The only real knock on the 770 is that in its price category there are better options in my opinion. The Ruger American, savage axis, and others are all similarly priced but better rifles in my opinion.
A 770 for a truck or loaner rifle, or even a budget rifle to help someone get into the woods isn't a bad thing. But there are some better options out there.
RIGHT NOW there are lots of good used rifles pretty cheap. Blued and wood just isn't that popular so you can usually find older savages pretty cheap. I've seen marlins in the 350 range lately.
I've picked up savages and Stevens for under $200 in the past and they are a much better rifle than the 770. Not a knock on the 770, it's just there are better options out there. If you have or find a good deal on a 770 I wouldn't hesitate to 'pull the trigger' and play around with it some.
-Jake