I've been for a ride in a 0.9 W453 (the new ForFour) and it was OK. The turbo in it was very on/off though though wherever that was the enthusiastic driving I don't know. I am aware of someone on one of the Smart forum having done a cross Europe trip in one but it felt and sounded like "a city car" when I was in it (much like the various generations of the ForTwo in many regards).
The 454 on the other hand (the old ForFour) feels that bit more special to be in, especially when the VVT engine howls past 3,500RPM before the gear switches up at the red line (in a AMT) to do it all over again. Sure, it isn't as practical in a city but then again, it wasn't made for the city specifically and the W453/Twingo was.
They are, of course, different classes of car so the the comparison feels a bit like comparing an apple to a pear.