As far as fidelity to the source material goes, it seems that X-Men: Dark Phoenix is definitely leaning closer to the comics than X-Men: The Last Stand.
That said, the synopsis doesn’t say anything about whether or not the film will go fully cosmic, so it remains to be seen whether or not rumored alien plot elements like the Shi’ar Empire will appear.
The 1990s setting, as well as the fact that it will actually go into outer space should make fans very happy.
The emphasis on the emotional connection between Jean and Charles Xavier also seems like a significant point to focus on, as the chrome-domed leader of the team will likely feel a deep sense of remorse and regret over what eventually happens to her in that storm.