The FEW things Wikipedia is good for, getting plot summaries to games a day after release.

Spoiler if you care, TDLR:

Had someone inside your crashed ship so when it explodes, tragic death. Also has the crewmate that dies in the beginning as the Necromoph that infects the Valor and kills Hammond.

Added more back story to Issac and Nicole, his mother was a Unitologist, Nicole said said she was safe, mother commits murder-suicide on father so relationship strained as she is a shit doctor

Story changed that Mercer, Kyne and Nicole were studying Necromophs than the marker as in the original, the focus was the marker to the point the captain used the ship's ADS to shoot down ANY ship to stop the outbreak reaching the ship, one got through (Dead space Downfall)

Instead of Nicole being a pure hallucination made by the marker to manipulate you, it's actually Cross and she see's you as Temple by the Markers influence.

Mercer dies like a bitch than in the original WILLFULLY allowing himself to be turned

The secret ending implies Issac WANTS to build a new marker, than as shown in the second, he first wants to stop the hallucinations but when that plan turns out to be a lie, decides on plan B, destroy the marker which the hallucination allows him to get closer to it to try to kill him (the marker fails). The new marker was only made thanks to reading his brainwaves by that needle machine so by force not willing.

After reading this then looking at a few clips on YouTube, it feels like it's not a bad game but less than the original with unneeded explanations, backstory and plot contrivances. The original had a lot of ambiguity and that added to the thill and tense atmosphere. This also not just negates the originals ending BUT completely destroys Dead Space Downfall which was a good animation showing how everything went to shit and also destroys Dead Space Extraction too by adding in these plot changes.