Our ST is going next weekend, replacing it with an Octavia vRS as my wife is expecting.
Totally regretted buying it. Made the decision based on a short test drive, really good price and glowing reviews, but on the first long drive (5 hours+) by an hour in I was considering turning around and picking up my older Fiesta Zetec-S or my Elise, even with 4pt harnesses and no radio I'd have genuinely rather have done the trip in it.
Ended up carrying on and passengering home in the back because the front seats were crippling for me. Poor ride quality didn't help, but the excessive lumbar support on the seats and lack of adjustability meant whenever I drove it I was stuffing coats or jumpers behind my back, but never found an arrangement that was comfortable, merely tolerable.
In terms of driving I never rated it, the front axle couldn't cope with the torque over anything less than perfect surfaces (eg. every road in Somerset), numb steering didn't help in terms of feeling what the front wheels were doing and it was very darty on initial turn in which it couldn't quite sustain once the suspension had loaded up - the electronics did a surprisingly good job of holding the car on the edge, but switch them off and it always felt incredibly nervous and borderline unstable mid-corner, particularly in the wet.
To drive quickly I actually MUCH preferred our old Mk6 Zetec-S - a slower car for sure, but far better feedback through the wheel and a chassis setup which flows over the surface rather than feels like it is fighting it.
Engine grew on me a bit (I utterly hated it at first), but I prefer a more linear power delivery and the low-end torque made it very easy to scrub into messy understeer as you exited a corner. People suggested looking at the Mountune kits and others, but looking at dyno graphs these mostly seemed to enhance the low-mid range whilst leaving the top-end a little flat so never explored it further as seemed it would just exacerbate the issue.
Positives were it looked quite good (for a small hatchback) and it was reasonably economical (averaging 39mpg over 20k miles or so, mostly by the OH), other than that I don't have much good to say about them.
The seats were BY FAR the worst part though - having something which made the car so fundamentally unpleasant to be in for even a short time then shone a spotlight on every other niggle you might otherwise look past or learn to drive around.