Excuse the snotty response,hope it didn't come off that way.
It's hard to qualify exactly point by point,but I think you just play a game and get whether the dev put some real effort into the game or not. Maybe it doesn't look as technically good but is well polished and plays good for example.
If I could more specific I would like to see the level of graphics in games like Metroid Prime2 and RE4 become the norm and not the exception. And hopefully a little better. Certainly I would like better than PS2 graphics because IMO GC was already better than PS2 is some ways graphically. If PD can make Grand Turismo 4 look the way they did on PS2 I see no reason why that level of graphics and type of game can't be seen on Wii.
Control wise that's harder to pin down because as you said we don't know exactly what the system is capable of.
We should at least see X-Box level graphics soon. It should go a bit beyond that (depending on how popular the Wii gets).