It's a very good controller. I don't know the current price, but I got one with my system for like $35 bucks and feel like it was VERY worth it. It's fought over by any of my friends, over the Gamepad or the Wiimotes/Classic Controller combo.
That being said, I personally have grown to love the Gamepad, outside of Nintendo nonsensical focus on trying to also make it a motion controller with some games (thankfully, you can usually get around that easily). I love heavy controllers, and it is the heaviest, I love that you can, like you said, plug it in at bed and play games on there. Over Thanksgiving, I took the Wii U home to my Mom's, and it was great to have the option of using the Gamepad only if need be. It's a really, really great system.