I expect a driver to get me from A to B, and notice whether I'm interested in talking (in which case talk and be friendly) or not interested in talking (in which case don't talk please).
A half-pint of water is nice but hardly necessary - it won't convert a horrible ride into a great one, and its absence doesn't make a great ride a bad one.
So much is outside the control of the driver - a late night drive with no traffic is generally more pleasant than a sluggish rush-hour drive, but it's not the driver's fault.
I once took a longer Uber Black ride to pick up my wife a few towns away, who was quite sick. Once I mentioned this to the driver, he drove noticeably more 'efficiently', offered me his phone to call to check on her once mine had died, and waited outside the building briefly to make sure everything was ok.
Also, I've got a bit of prior race driving experience, and this guy clearly grokked car control. I wouldn't be surprised if he'd spent a good bit of time on a track. He also, without drawing any attention to it in any way, adjusted the suspension settings from 'firm' when we were going around on- and off-ramps to comfort on the highway, to keep the ride comfortable and level.
I gave him a five-star rating and sent Uber customer support an email raving about him. Wish I could have done more.
I think it this case you did it right with a letter to customer service.
When the "expectation" is a 4/5 star rating, then the average is generally 4.6-4.7 stars and there's no way to distinguish "normal, good service" from truly "above and beyond".
Additionally, if the "above and beyond" just gains a 5 star review, that doesn't really give the feedback needed for extraordinary service.
In my experience with cab drivers if they don't offer unsolicited conversations about religion or politics that's an exceptional experience. When I say conversations I mean they just drone on and on one sided about how great God is and how Obama is ruining the country.
I expect a driver to get me from A to B, and notice whether I'm interested in talking (in which case talk and be friendly) or not interested in talking (in which case don't talk please).
A half-pint of water is nice but hardly necessary - it won't convert a horrible ride into a great one, and its absence doesn't make a great ride a bad one.
So much is outside the control of the driver - a late night drive with no traffic is generally more pleasant than a sluggish rush-hour drive, but it's not the driver's fault.