What are you referring to, specifically? Visuals? What did you expect? It's going to apparently be a dense city with "3D movement" (flying cars?). GTA V looks about the same, if not a little worse in some ways (probably better in others). And the game still needs to run (well) on the default XBONE and PS4.
PC, PS4 Pro and Xbone X users will almost certainly get some sort of additional "hi-def" option, or option(s) in the case of PC.
If you mean gameplay, well, this was just a teaser. They already said they're going to show more at their E3 2018 booth.
Remember, they said they'd let us know "before or at E3" what they were up to. Consider this a simple "We'll be there, and we'll be talking to people and doing other non-teaser stuff" (As confirmed by the Coliseum guy, and their hidden message).
Also, the aesthetics could change in the final release. They did in The Witcher 3, the 2013 trailers looked similar to Skyrim, while the actual game is much more colorful. It may even be intentional to attract the "GTA" crowd, it would not be an unusual approach to target multiple audiences. So, on the surface the trailer shows action, car chases and explosions, while the hidden messages reassure the hardcore fans that the game is still an RPG.
