Here's my opinion, being one who seriously considered an RX330 and XC90 as well as the MDX and other competitors.
The RX330 is NOT a value vehicle. It's expensive. At $50K, you do not get a lot of features that are standard on the competitors. Load it up like the competitor, and it's significantly more expensive. Is the Lexus badge worth that extra chunk of change? Granted, the RX is a great SUV, superb fit and finish, quiet, and very smooth. The cargo space is not large, the intrusion of the wheel well/armrests results in a loss of usable space. The sliding rear seat is a nice touch. Lack of a sunroof for a $50K vehicle? Laughable.
The MDX, which we purchased, and at $50K, got me a lot more features. Loaded, the MDX only had one option package, nav/dvd/rear camera....add that to the Lexus and see where the price is. The MDX is not as smooth, but is larger, and just as comfortable. The MDX's larger size doesn't make it as nimble but it soaks up bumps just as nicely as the RX (probably a bit better as the lower profile tires on the RX did not do as good a job with road imperfections), but the RX handles better in corners. The MDX leans a bit more than the RX does.