In general i've come to realise the IS200 is much better at higher speeds than slow. When you have the space to clearly pull through the gears at your own pace its lovely, and even the feeling as you rise up to 90mph in 5th gear and the VVTI kicks in, it starts pulling again more than most other cars would in 3rd! and being that japanese bred engine it does love to scream if you get a bit viscous with it.
However, i find it difficult round town, its not the easiest car to constantly be starting and stopping in traffic - you'll have to train your feet to be very smooth and accurate.
Its more than enough power, it'll just take you a little while to realise it - then by this point, you'll start appreciating the other qualities of the car.