Having had the RX for a couple of weeks now, I find myself echoing most of Spacewagon52's comments from his excellent review, so figured I should add my two penn'rth to this thread.
Comfort: It's like driving around on my sofa. The seats are amazing (and the seat heaters are welcome). Ride isn't quite as supple as my Audi A8 was, but that had air suspension, so understandable. Still very smooth, though.
Audio system - mine isn't ML either, but it's at least as good as the Bose system I had in the Audi. I'm using a bluetooth-to-FM widget for streaming music from the iPhone, which works adequately.
Economy: Not too bad, considering,. My A8 was V8 powered and would do just over 30mpg on a long run if I was careful. The RX does slightly less on a long run (high twenties), but average day-to-day driving is no worse. I don't do a lot of mileage, so that's not an issue.
Handling/Performance: it's a bit of a bus, but easier to handle and nicer to drive than other SUV's I've tried *cough* Range Rover *cough*. Performance is fine for what it is - all fairly effortless and wafty, which is all one needs :)
Keys: Far too fragile. Had to rebuild both using the kit from the guy on ebay who supplies pre-cut replacement casings. Easy job and not expensive.
Like Spacewagon52, I find myself missing having parking sensors (I don't have the reversing camera either). A retrofit is on the cards.
Power tailgate: very handy indeed.
For such an old car, it's superb. I'd been tempted by a (newer) RX on two previous occasions, both times ending up in Audis instead. Glad I finally bought one - it was the sensible purchase for my current circumstances, but one that I'm enjoying out of all proportion to the low cost.