The design has clearly evolved since then, but how? Some enthusiastic designers at PartCatalog.com have created a GIF (above) that shows the difference between the first model unveiled in May, 2016 and the final production model that Elon Musk flaunted a few days ago. (Bear in mind that differences in camera angles, color and other reasons may exaggerate or minimize the differences.)
The front end in particular has been tweaked, something that's a bit easier to see on this Reddit post from April showing a spy photo of a nearly identical vehicle. The Model 3 is now a bit longer and lower, has redesigned headlights, and features a more deeply sculpted bumper cover. The front wheel has been pushed forward a bit, and the back end is a bit bigger and higher.
That changes the aesthetic (for the better, in my opinion) and may give folks a bit more trunk space, both in the rear and forward "frunk." Tesla may have also made the changes for safety, performance, production or other reasons (we've reached out to Tesla and Musk for more info).
Overall, the tweaks aren't a huge deal, but it's interesting to see how Tesla thought about this. After having production problems with the Model X in particular, Elon Musk vowed to keep things simple with the Model 3. As such, the design changes might have been prompted more by production and quality-control concerns than aesthetics. The company is estimating mid-2018 deliveries for new pre-orders, so it has to build around 400,000 Model 3s in just 15 months.