I own one. The only problem is all the naysayers who think that because it is a BMW it is automatically overpriced, or that you must be some sort of elitist or something. Jealously is so sad 
It has been very good. A few minor electrical hiccups that were easily dealt with under warranty. At the time we bought it (2002) there was not much out there with similar interior luxury, although now you have the Porsche and others. Most have a little bit more hauling space, which I always think would be nice, but then it has always fit everything I needed it to. I have the 3.0…I drove the 4.4 and could tell very little difference, in fact around town you probably wouldn’t notice much at all, it is more of a factor in passing on 2 lane roads. The 3.0 does fine there too but you might have to wind the engine up a little more. If you want fast accelleration or great cornering, the 4.4 isn’t going to get you there, nor the 4.6 for that matter…get a real sports car.
Why is it worth it? Well, I paid about 49K, base was 39K. Compared to your 30K SUVs, I have a vehicle that has a much nicer interior, GPS, wood, leather, climate control, auto-everythig, is very quite, handles better, looks nicer, has a longer warranty, included things like dynamic stability control (which may have saved my butt when I recently had a blowout at 85mph), a “good enough” all wheel drive system, smoother engine, better handling, etc. If these things don’t matter to you, then buy your GMC and be happy. Note that this is getting to be a fairly old design, so a lot of the competition has caught up now and there may be some other good choices. I also have a 325i with 100K miles on it and very few problems…in my opinion these cars are pretty well put together. You really can’t compare it to something like a Honda Element in my opinion.
BTW, I also own a Porsche 996 (water cooled 911). It basically does everything better than any of the air cooled 911’s did, as admitted by many who own both. A lot of people like to rag on Porsche about this, but its a technological no-brainer…the only reason to stay air cooled was “tradition”. More power, lighter weight, what’s not to like?