Unfortunately, it was pouring rain on the second day of my rental so I didn't get to take it up in the mountains, but I did get a decent sample in the first day. Since my daily driver is a C350 I find myself using that as a benchmark. My impressions:

• I found the engine to be competent, but not exciting. Stomping on the gas resulted in quite a wait to really pick up steam. It's not a low-end-torquey kind of engine but isn't a high-rpm-screamer kind of engine either. It's just... not quite enough to be fun in any regard. More than ADEQUATE mind you - just not fun. Highway passing is probably the worst culprit. You really notice how heavy this vehicle is.
  
• The C-pillar blind spot over the driver's right shoulder was particularly bad.
  
• The handling was generally good. Contrary to some other reports I have read here, I thought the steering feel was quite good. Plenty firm - any firmer would have been bothersome. Though much firmer than my vehicle, it transmitted less of the road surface feel (in California read: bad pavement jitters). The suspension also absorbed some of our worst sections of highway with ease - but in a much more firm an controlled way than the old Cadillac "floaty" land yachts.
  
• Side bolstering on the seats was excellent.
  
• It amazes me how much higher off the ground this is than my C350. I am at least 4" closer to the ground in my car. This, the quiet interior, and the stiff but non-conductive steering lead me to feel like the Caddy is optimized more for comfort. Getting back into my car afterward felt like getting into a turbocharged go-cart.
  
• Cadillac REALLY needs to go hire someone to clean up their ergonomics. A/C controls behind your knee? Really?!? And the controls for the trip information system are located behind the steering wheel and there is no way you can operate them without looking at them, requiring you to lean forward to look behind the wheel at them. Traditional GM oversight. Radio buttons were a giant disorganized mess. I did appreciate actual physical buttons for the radio presets even if the display attached to them felt very Chevrolet.
  
• That is a big honking square remote - and the key isn't integrated. Either ditch the key and make that square bad-boy keyless across the model line, or use a remote-key combo that doesn't take up half your pocket. Problem intensified by National strapping both keys and both remotes to the key tag as is typical.
  
• Every Nissan Altima comes with Bluetooth stereo capability (even if their method of configuring it only via voice commands is the world's most annoying). Come on Cadillac - don't you think you could spring for Bluetooth in this vehicle?
  
• While we are on the radio, someone needs to tell Bose their car stereos aren't any good. I have seen the same results on every Bose car stereo I've used, from the DTS to the Corvette. Try though I might with the equalizer controls, I was unable to make the lower-midrange/upper-bass sound like anything but soggy cow manure. They mistake distorted booming upper-bass for clear, crisp full-range capability.
  
• Comically, I could not get the windshield wiper interval set to my liking. Cadillac (like Mercedes) doesn't have a true intermittent setting. It goes "Off, adjustable rain-sense, low, and high". So even on the slowest intermittent setting the wipers would kick into overdrive every now and then for seemingly no reason in light rain. MB does the same thing - though probably not quite as drastic and schizophrenic in their execution.
  
• Interior materials have improved drastically at GM in recent years. I still saw some annoying fit-and-finish flaws in this vehicle. The grille set at the center of the dashboard near the window was crooked (protruding above the dash on the right and recessed below the dash on the left). It is such a bad place to have poor quality - you sit there and notice it the entire time you are driving. Also, the door trim didn't quite line up with the dash board - particularly on the passenger side in my vehicle. Overall, though, the dash materials looked good and the center console materials looked average for vehicles in this segment.
  
• Trunk space is excellent for this size vehicle. At least 50% larger than my MB, and there is no hump over the rear axle eating into the trunk. The space is deep and flat.

You can find the pictures in Zoidberg's 3.6L review - I don't bring a camera and it was miserable weather outside anyway. I look forward to having a second impression in drier weather.