It's functional and (for better or worse) kind of unique. Like others have said, it really depends on the game. Wiimote on it's own; fine for motion control stuff (if you like/can bare motion control stuff), but pretty awkward used as a traditional 'vertical' controller. Wiimote + Nunchuck; usually fine, but massively depends on it's implementation. Wiimote as a lightgun; pretty much requires a 'gun' grip to not be uncomfortable. Wiimote + Classic Controller; If I can't use a GC controller then this is my default... but it will never not feel weird having the Wiimote tethered to the controller I'm using.
Not Nintendo's worst controller is probably how I'd sum it up.