This is a sad subject for me since I was 50/50 between an N and an ST.
I sat in a showroom only ST today at a showroom unveiling in Frankfurt and was only semi impressed. Interior build quality is marginally better than an N. The Recaro seats are nice though and the screen is noticeably better. Exterior is truly on point, it is a sharp car!
However, I have a friend in the states with an '18 RS that has nothing but motor issues. Also 3 friends here in Germany with new model year Focuses have also had sever motor issues (yes, I know the new ST has a revamped 2.3 which is different than the range of lower models). I have read a lot of articles about the focus being a great drive but also having quality control issues with engine components.
After seeing the new ST I was pretty disappointed about paying 43,000 Euros (fully loaded) when I can get an N for 30-32,000 Euros and have (generally speaking) the same car.
I have owned 7 Ford's since my 1990 Ranger including an ST and RS and never had a problem. Although I am going to wait for a test drive version before I make my final decision and purchase I would have to say Ford dropped the ball on the ST. I'll keep those interested posted after my test drive and let you know how it felt.