Enjoying the new 3 Series GT quite a lot. I know it's a very mar-mite type of vehicle, with some hating the way it looks, and others thinking it has no place even existing, but personally I think it's absolutely ideal for it's very specific market, that is those who want something roomier inside than the other 3 series models (and even the 5 series!), but retaining the large boot capacity and overall economy, as well as that level of comfort.
Space.
It's weird to me that the 3 GT has more legroom than the 5 Series, and more boot capacity than the 5 GT. If internal space is a real consideration, eg you have a big family and/or need added baby seat plus passenger space, as well as a roomy boot for the pushchair plus shopping etc, the 3 GT is pretty much ideal. More than near enough every other model BMW offer minus the 7 series, which is strange given it's confined to a 3 series model. Overall the cabin is just extremely spacious and comfortable, and has an almost 7 series limousine esque aura about it, only minus the even more ludicrously luxurious and elaborate looking leather and instruments. But the legroom in the car really is massively generous, and the boot space too.
Ride.
Ride wise, I guess it's sort of like a combination between a BMW sedan and SUV. Not quite as nimble as the regular sedans (though certainly very close), but with the added benefit of a higher ride height. extra comfort and added visibility. It feels slightly more executive as a result, whether you prefer that or not will be purely subjective, but it's certainly quite a unique driving experience, and in Sport/Sport+, it still tightens up and gives you added precision. The steering is also a little heavier than the 3 series, and even compared to the bigger X5. I also find the cabin very quiet overall, with little in the way of vibrations or drama.
Issues and surprise positives.
My biggest complaints at present would be the visibility from the rear windscreen, which is quite small, as well as the lack of a rear wiper (still not a big issue). I also find the heating takes a bit longer to really fire up than I'd have liked, but that might just be because lately it's been really cold (around freezing temp).
There's decent little touches that I didn't expect, or didn't expect to enjoy as much though, like the one pull rear seat drop, the as standard automatic boot, the overall excellent fuel economy, the rear spoiler which can be activated at any time, the frame-less doors, the quality of the sound system, which is better than the X5's BMW Advanced Set up, and so on. BMW has definitely done well to improve the audio quality, because before I felt some of their systems were far too bass heavy, and not articulate or accurate enough. Whilst before I found the new Mercedes, Jaguar and even Hyundai's optional advanced sound systems better overall, now BMW seems to have caught up. I honestly don't think the Harmon Kardon upgrade is even necessary. Hell I use Sennheiser HD800 and Beyerdynamic T1 headphones in my home set up, and to get the 3 GT's sound balanced, only a very slight EQ is required (slightly increased treble). Comparatively in the X5 I had to reduce bass in a big way, as well as drop the mids and increase the highs.
Overall, at this point and time, I'm not really sure why anyone would buy a brand new 5 series over the 3 GT, at least right now, unless they really hated the way the GT looked. I am however confident the new upcoming 5 Series, which should see a refresh soon, will be a big improvement, and easily one up the 3 GT in nearly every regard (besides price).
I will also add that the company cars we have are all much faster than my personal car (naturally with them all being 3-5 ltr engines and much higher spec), but I wouldn't exactly say the 320D is slow. In Sport+ with Sport Auto or Sport Manual enabled, it still puts out respectable enough performance, at least for everyday driving.
Lastly, I really do think the M Sport version is a must. Without it, it just looks even more bloated and less aggressive.
3 GT vs 3 Sedan track times compared
On a side note, I saw this video where the 3 GT's track performance is compared to the 3 sedan's, both 320d variants, both non M Sport, and surprisingly enough, despite the GT's extra weight, size and bulk, on the track it was only 0.9 seconds slower overall. With a best lap time of 2:40.2 vs the sedan's 2:39.3. Pretty crazy when you think about it.
3 GT vs 3 sedan lap time comparison
The earlier 3 Series sedan test.
BMW 118d & 320d @ Buddh International Circuit