A fabulous car. My previous car was BMW 320d and it was a good car, but the 520d is a substantial improvement in every area.
I was worried that the Msport spec would give it a hard ride, and although it's a bit jiggly at low speed over bumps, it smooths out at motorway speeds. The speed with which corners can be taken is remarkable, and the car remains level and composed up to remarkably high limits, which means that if you just drive it briskly under normal conditions, then you have quite a reserve of grip to cope with tighter than expected corners. In addition the 18" wheels and body kit give the car a more sporty M5 (esque) look.
Initially the car felt a bit under powered, but the engine has loosened up recently, and whilst the performance isn't electrifying, it's adequate in 99% of cases, and it returns 45mpg, and the lower the emissions, the lower the company car tax liability.
Compared to my previous 320d (2005) this car has a more even spread of power. This car has slightly less urge between 2000-3000rpm, but now now pulls eagerly and with power round to the 5000rpm limit, making it more petrol-like. On the previous car, the onset of stalling was very sudden with no warning and hence no chance to balance the clutch and throttle, but this model seems to intervene with a burst of throttle, with the result that it's quite difficult to stall, which is good. It will also pull away from walking pace in 2nd gear unlike my previous car.
To drive on a long journey the car is joy; quiet, refined and relaxing. Build quality appears to be good, and the quality of the half leather/clothe seats looks good as well.
The boot is large, with two storage compartments underneath, although I am not sure how useful these are, but they do ensure that you have a lip-free loading area. As per the 3 series, BMW have painted the section of the rear bumper next to the boot, which means it will scratch when sliding heavy items in. Previous BMWs used matt plastic here, and Audi use stainless steel, which is far more practical.
My only gripe is the 12v cigarette lighter sockets. As I regularly use a satnav and phone charger, I need two sockets. If you plug anything into the front ashtray socket, it bangs your knuckles when changing into 5th gear, and if you leave a charger plugged into the rear seat sockets, people entering the rear seats often kick the charger, ripping the charger and panel out. My solution has been to wire a 4 way adaptor into the rear sockets, from behind and then put the adaptor inside the centre arm rest. Why BMW couldn't have better located the front ashtray and added a socket inside the centre armrest (like the 3 series) I don't know.
Overall it's a great car, and please consider it before buying a 3 series. It's so much better and not much more more expensive than a 3 series.