Is it a remake, or a remaster?
Erm... it's complicated. The original Mass Effect game has received a more substantial touching-up than Mass Effect 2 and 3, primarily around the combat system and UI. This makes sense, as the first game was more of an RPG and the sequels greatly improved the combat: so Mass Effect 1 is receiving something of a rework.
The game's UI and various interfaces have been overhauled, and combat and exploration brought in-line with the sequels' improvements: better aiming, squad controls, team AI, and camera positioning. On the last point, for example, you'd commonly take cover in that game and get a brief view of the interior of Shepard's skull: no more. Finally, and perhaps most-wanted of all, the handling of the Tonka-like Mako surface vehicle has been overhauled. I always hated the way this thing drove, so good news.
That aside, there will be no big changes to the adventure itself. At one point there were discussions about pursuing a more ambitious route, technologically speaking, but that would have put Bioware in a position where, essentially, the games were being rebuilt from scratch.