Ha, I bought a 335d to replace the S4, I am not at all disappointed, it is quicker than the S4 (actually quicker than the old RS6 and RS4, and is also the quickest diesel you can buy!) it will do 0-60 in 4.5s and I get 38mpg out of it driving it the same way as I drove the S4 when I was getting 19mpg!
If a 335d is an option I would recommend it, if you are buying it on finance you should look at a new one as a decent bit of haggeling can get you about 18% off the list price!!
I do still miss the V8 though.