Tom bought a B250 so maybe he can chime in with his experience so far.
http://wildsau.ca/2014/08/review-2014-mercedes-benz-b250/
Hey everyone - yep, that was our own vehicle in my review.
It was my wife's daily driver when we bought it (it has been replaced by a 2014 E63 wagon, so the B doesn't see as much driving now but remains part of our family) and we've had it for about two and a half years. So far it has been flawless, in terms of quality and reliability. We pre-purchased the (rather expensive) service package, which saves us a ton of money on the first 4 services, which will take us through the first 4 years of ownership, at which point we are likely to replace the vehicle.
Fuel economy has stabilized and averages at around 8.8 L/100 km with virtually all city driving. The car has been on the highway literally three times in its life. As an urban warrior, it really excels. Easy to drive, comfortable, efficient enough, plenty of power, lots of room in the cabin and in the trunk.
Obviously I would prefer to have the current 4Matic version, but we've fared very well with good winter tires and if I had to choose between winter rubber and AWD, I would always go for good tires. So we have no complaints with our front-wheel driver in the winters. The run-flats that come with the car are the biggest compromise. The hard sidewalls make the ride quite harsh over bumps and God forbid you meet a pothole. I recommend replacing them immediately with good summer tires and good winter tires - we actually got surprising credit money from the tire shop for our brand-new run-flats that they took in trade. It makes a big change in the vehicle's road noise and ride quality.
Is this an E-class? Of course not, and Mercedes doesn't sell it as one. It's a nice little MPV that works very well for small families. We have three kids that spend about 5 minutes in the car each way (to and from school) and we can easily get them all in the back comfortably for a shopping trip too. I would hesitate to take more than 4 people on a road trip in it, but that's not an issue we have.
If it had been available as such, I would have bought it in all-wheel drive (4Matic wasn't available for our model year) and with a diesel powertrain (only Europe gets those - the B250 is the top-of-the-line there, and when we were in Europe the summer after we bought it, people thought we were totally rich because we had bought the Richie Rich petrol B-class - haha!) One thing to note - as with other brands, you'll find incredible rebates/reductions on MBs at certain times of the year. We've seen $10,000 off the B-class price in our newspaper when the model year is coming to an end. That makes it a much better entry price.
I would absolutely buy this car again, and had we not come across a stellar deal on my wife's new daily driver which was also her dream ride, she'd still be driving it every day. She loves it and sometimes opts to take it out instead of her E-wagon.