I recently went from a BMW 328i to the FX35. I needed some of the functionality and all-weather capabilities of an SUV, but also wanted to have solid performance and distinctive looks, and the FX35 has been a good compromise for me.
I used to really enjoy the performance/handling of the Beemer, and although the FX35 can't match that performance, it does way better than any other SUV and is really quite enjoyable to drive. The only area where I have seen a marked difference is in braking - I'm not sure how the braking distances compare, but the FX35 clearly has a lot of heft which is apparent when you're trying to slow the beast down.
On functionality, it doesn't have as much room as most SUVs, but has quite enough for my needs. I've used it to haul a freezer, and even some good-sized wood planks (by pushing the drivers seat as far forward as possible), and it has served me well. I simply don't need it to do everything that a full-size SUV could do.
On all-weather performance, the FX35 with stock tires did really well in the rain. I opted to get snow-tires for the winter and it's been very solid so far (it has already seen a good amount of snow, although nothing crazy). It's definitely waaaay better than the Beemer.
On looks, I had and still have a particular soft spot for that Beemer (and yes, I value the BMW brand cache highly), but I also really like the looks of the FX. It evokes extreme reactions - some love it, some hate it. Luckily I'm in the former group.
With heated seats and the tech package, I also love all the "extras" in my FX. And despite all the talk of rattles on this forum, I think the Beemer was actually more prone to rattles (I am not used to and don't expect the absolute perfection that other people seem to expect).
All in all, I wouldn't get the FX if my needs were squarely sports sedan or if they were squarely SUV. The reason it works for me is because I wanted a bit of both. The FX is really the perfect crossover as far as I am concerned.