Far superior car. After owning several Model S cars, I finally decided to give the MUCH CHEAPER Model 3 a try. Pretty much hated it from day one! Not to put anyone off of the Model 3. If you haven't owned a Model S, then you won't know the difference and the Model 3 will likely be great for most coming from other types of cars. However, for me, I was spoiled with the Model S. I gave it an honest try with the Model 3 for about 8 months. Finally ordered a new S. My first "Raven" version and WOW. 5 miles in, I was instantly at peace, relaxed and said "I'm home". It was worth every penny to upgrade back to the S, for me at least.
The Model S is just a far superior built car. Aside from it's obvious size difference, the quality level is clearly apparent.
Interior MUCH quieter on the S.
Seats far more comfortable.
Air Suspension produces a gazillion times better ride than the stiffer Model 3. (many will prefer the sportier ride of the Model 3). Personal preference. With Air Suspension though, I have a choice for a nice cushy ride if I want it, especially appreciated on long trips. Or, I can stiffen it up for a sportier ride too. I love having the option.
My Model 3 didn't have key fobs, was a huge deal for me as I hated having my phone as a key. This has since been corrected, but was one of the big reasons the 3 annoyed me so much.
Model 3 also now has an automatic truck, which mine didn't. Although, I prefer the hatchback and added space afforded, not just from the size, but from being a hatchback.
For me, I hated everything being controlled in the center screen. Did not like the Horizonal layout. Much prefer the vertical layout where everything is easily readable. Things on the far right of the Model 3 screen are difficult to see at quick glance while driving. I love having my navigation instructions directly in front of me, especially on the tight winding roads I am commonly on.
Little things, like having a simple glove box button was a big deal for me. Much prefer the additional stalks.
Personal preference, I like the wider stance of the Model S. Hated the headlights on the Model 3. Rest of the car looked OK, but was too narrow for my taste.
I also hated the door handles. My hands are commonly full and I love being able to open the Model S with my pinky (all that I have available without setting things down first). Model 3, had to free up an entire hand to open the door.
And again, just overall build quality. While all Tesla's do not remotely compete in terms of actual "Luxury" with the high-end brands, the superior build quaity of the Model S drives more competitively with the higher-end brands. Just a more solid feel in general. The Model S feels like an $80,000 car. The Model 3 feels like a $40,000 car.
Again, most are simply just my personal preferences in a car and what's important to ME. The Model 3 certainly has a technological marvel and really isn't missing much in comparison to the 3, which is what appeals to most seeking to enter the Tesla world. So in that respect, you won't be disappointed with a Model 3. But, if you're coming from a Model S, and any of the above is important to you, or if you love the quality of a larger Mercedes, BMW, Audi, etc, then the Model 3 could disappoint. Just sharing my firsthand comparisons for those that might have similar preferences and tastes to my own.