We took delivery of a Model 3 four days ago, and I've owned a Model S for nearly five years. My current P85 is 3.5 years old. So it doesn't have AutoPilot.
The Model 3 is a great compact car. It's light. It's very nimble and handles turns beautifully. It has a great turning radius. It accelerates very well. And the stark alien spaceship like interior is stunning. The single slot air conditioning is super cool. And yes, the screen is really sharp. But to think that this car is better, or even comparable, to a Model S is IMHO delusional.
The Model S is an ultra-high end luxury sedan. It is smooth as silk on most any road. In the Model 3, you can really feel the road, and not in that Porsche good kind of way. The 3 is a compact car that weighs about 1000 pounds less. The Model S cabin is virtually silent. The Model 3 lets in way more outside noise. The Model 3 has plenty of acceleration for normal driving, but it's not close to my P85. Did I mention sun roof and air suspension?
UI/UX is sometimes in the eye of the beholder, but I much prefer the MS. The Model 3 doesn't have an internet browser, and no big energy screen like the S. I like instantly seeing my mileage on my current trip and since my last charge. My S can have that visible all the time. The Model 3 requires several clicks and swipes on the screen to view it.
The screen on my 2017 Model 3 is much sharper than on my 2014 MS. Duh. Some of that is that is because the navigation screen is much smaller, and most is probably because screen technology on tablet devices has gotten much better. Maybe a 2017 Model S has a better screen than my MS ? Dunno.
The Model 3 is different than the Model S in many respects, and for some people those things (price, size, mileage, nimbleness, stark interior, turning radius) are most important. You might find that the Model 3 features are a better fit for you because on those things I believe it beats the MS.
In summary, I think the Model 3 is a great car. I have test driven a BMW i3, a Chevy Bolt, a Mercedes B200, a Ford Focus Electric and I owned a Nissan Leaf. The Model 3 is light years ahead of any of those.
about the UI thing its not really up to the eye of the beholder the number 1 rule in human computer interface design is least clicks to accomplish your goal. In the case of the 3 vs S the 3 ALWAYS has more clicks and has a more room for error since it is all touch screen so it is infact inferior.