My dad had a S4s up to last year, sold to my brother in law (well sisters partner of 15 years still unmarried!).
I've had to drive it on many occasions, especially come service time/problems with Lotus specialist very local to me (Chris Foulds Motors)
Yes very fast, but not as fast as the Maser though.
Really, over the 8 years he owned it, loads of trouble, and yes usually serious .
Steering rack (twice)
Exhaust manifold gaskets
New Turbo
New flywheel (and clutch)
A/C problems
Battery drain problems
ALB sensor problems
Instruments falling out behind dash
Interior rear view mirror falling off
Gear shift cable problems
It was not maga mileage at around 50K either, if a V8 it would have been worse, according to many indies!