8spd auto here, sublime gearbox mated to the perfect engine IMO.
Reliability has been faultless in the 7 months I've had mine, covering some 5,000 miles (currently at 40k). However, I'd not buy one without either BMW's used or new warranties.
It makes me grin every now and then, sure, but normally because of how much pace it has in a straight line. The other times, obviously, it's just a 1 series. Which means it's pretty naff. It ultimately depends on what you're coming from, as my previous motor was a 2004 330Ci so obviously the M135i is a far newer piece of equipment in many ways...
BUT!
The 330Ci has/had much more character, more soul etc. I've not really bonded with the M135i all that much, it's just stupidly competent at what it does. Just don't go in thinking it's an M car, it just isn't. It grips and corners well enough but it doesn't necessarily egg you on to go further.
I'm sure others would disagree, or advise modifying with the car a little (which I have no doubt would cure some of my issues with the car), but I prefer a stock experience.
25-30mpg on my 10 mile B road commute, YMMV. I've yet to do any servicing but since the costs are pretty much fixed, so go figure.
Option wise, get the Pro Nav as an absolute minimum.