It's early days for me and the S4, and plenty of time for MANY EXPENSIVE THINGS to go wrong with it of course, but I'm honestly prepared to say based on my time in it so far, that it's the best car I've ever owned.
It really is two cars in one, stick it in dynamic mode, set off for some 'spirited driving', and it's an absolute beast of thing, with truly gob-smacking pace and superb cornering ability. I know Cavey doesn't much rate the handling on these cars (and yes they do understeer, but the newer ones with the V6 are nowhere near as bad as the old V8s), but I've been driving the mountain road here for over 16 years, and this car handles it with aplomb - it feels as well planted on the road as the Scooby did.
However, leave it in auto mode, and it's pretty much just a normal everyday practical saloon car. Easy to drive, quiet and comfortable - with a handy burst of acceleration when it's needed. (Comfort mode is a bit too squishy and wallowy IMO, auto gets the job done for everyday driving fine.) I was off last week so did a fair bit of driving around with Mrs Hearthly in the car, she found it comfortable and pleasant, and was pleased with the heated seat
The B8 (2009-2015) S4 got a facelift and tech revision in 2012 (not sure on the exact model year but they're easy enough to spot), but even on my earlier 2010 car it's got all the toys and tech I want. In particular I love the dual-SD slots in the head unit, and the factory-fit iPod/USB connectors in the glove compartment, all of which are fully integrated into the MMI system. (I've got 144GB of music on tap via an iPod and two 32GB SD cards.)
I've already put several hundred miles on it, and it looks to be settling down to about 25mpg with a combination of driving styles, so not bad at all for a car packing 333bhp.
If you're seriously starting to look at these asfish just let me know as there are definitely a few options you want to be keeping an eye out for IMO. Specifically the Drive Select was an option on the pre-facelift cars (it's standard from the facelift onwards), I think you definitely want this. Also the MMI wasn't standard, which is pretty scandalous considering how expensive the S4 is even in its base configuration (£37K without any options at all), I think you definitely want this as well.
When it comes to the looks of the car that's subjective of course, personally I really like the fact it just looks mostly like a normal A4, with a few key differences if you know what you're looking for. White is a nice colour but fuck me they pick up the dirt and show it, very quickly.
There seems to be a reasonable number to choose from looking at sites such as Autotrader, so you can afford to be picky in terms of getting the one you want when it comes to colour/options/miles/price etc.