I have a wiiU and love it, but some points in which I disagree.
1 - If you value Nintendo games in HD then wait until next year to buy WiiU as there's nothing here for now, even Pikmin (my reason for buying the console) got delayed and has no release date yet. No 3d Mario yet, no Mario kart, no Zelda, no Metroid. Unless you love zombiU (as I do) then just wait until at least Pikmin.
2 - Off TV play, while cool, it's nowhere near important to me or many people, some of us either dont share a TV, or have several TVs, I would not trade my 1080p 42inch TV with fantastic colors for a 480p 6inch screen with a bit dull colors. This might be usefull to some, but not everyone.
3 - The unique gameplay is fantastic, I love it, specially in ZombiU and Batman, it makes Batman completely better. But, many people might not like to look at a second screen.
4 - Your title concentrates on the gamepad, and that it delivers so here we go:
a) The resolution is way too low compared to phones/tablets nowadays, and it shows, games appear very pixelated and text is harder to read
b) Sound through headphones is a bit on the low side
c) Battery life is abysmal bad, as in 3-4 hours on middle brightness
d) Touch is unresponsive, I advise you to use your nails, it should have been capacitive touch
e) No analog triggers, which means, no proper racing games besides mario kart, you need the analog control for acceleration and brakes, it would be impossible to play a gran turismo or forza in this
f) Clunky gamepad, when it vibrates you can hear it, when you press the triggers you can hear it, unlike ps3/360 controllers, it just sounds cheap
g) For such a big gamepad its surprising to see such small face buttons compared to ps3
h) The biggest problem with this gamepad, it attracts dust like no other device ever, the other day it took me 5 minutes to clean the gamepad, it gets dirty very easily.
i) One other big issue, if in the future you need to replace this gamepad it will cost you over £100 so dont break it.
Now with all this said, bear in mind again the price of the console and the games, there hasnt been anything good released since November. Rayman legends, wonderfull 101 and pikmin 3 are the biggest releases for this console and all got delayed. Most games you can buy on other consoles for cheaper and the OS is still to be fixed. My advice wait either for games or for a price drop. I paid full price on launch, money is not an issue for me, but I dont think this console is worth the full price.