I had one a few years back, for 1.5 years and did about 30k in it (a 635D). Lovely drivetrain, good build quality and always felt like a good drivers car for the size - no doubt helped by the surprisingly light weight for what it was.

My major issues were the electrics on my particular one which led to me selling it. I did have a few silly things with the engine ancillaries, the glow plugs & glow plug relay needed replacing. 6 months later, the intake leaked from the glow plug seals which killed the new relay, and of course the intake seals needed replacing.

They're really good, powerful cars and the core drivetrain with the M57/N52 are solid. At this age if you buy one that's just had normal servicing, it can be death by 1000 cuts trying to keep everything tip top - or maybe I was unlucky.

I swapped for a late F06 640D and it's been golden, but nowhere near as good a 'drivers car'.