I had a new Model S 100D for a week and there's no doubt it's an interesting car. The performance is certainly there, and the software features on the big screen are nice and modern. That said, knobs and dials are much easier to use, Touchscreen is inherently flawed when it's in a moving car. The supercharger network seemed to all work nicely, but obviously for mass adoption there aren't nearly enough bays. And it's £24~ to charge up there, so not free as some would have you believe (unless you have an older model).
And while the electric performance is nice and instant, it doesn't fill the void of a nice rumbling V8, if you're into cars, that is.
However, the general quality is closer to a Vauxhall Astra than a premium German car for example. Lots of odd fittings and cheap plastics everywhere. It's not bad, but for the price, not good enough.
They look nice enough on the outside but a little bland, but that's obviously subjective.
As for infotainment, iDrive is perfectly fine and just as good for the most part, and much nicer to control with the wheel.
BMW certainly don't have much to worry about when they join the electric market properly. I wouldn't really want one over a current decent spec 530d, G30 or F10, certainly not for the huge extra cost.