Bioware has released an official comparison video between the original and the remastered version of Mass Effect. This video will give you an idea of the enhancements that the team has implemented in the first ME game.
As we can see, Mass Effect Remastered will have a new UI that is similar to the one found in Mass Effect 2 and Mass Effect 3. Moreover, it packs new lighting effects and new assets. The camera also appears to be closer to the character (so here is hoping that there will be a FOV slider).
Mass Effect Legendary Edition will have improved aiming and weapons balance. Additionally, the game will have better SFX, better Mako controls, input/controls, squad behavior, cover behavior and gameplay cameras.
It’s also worth noting that this trilogy will have some PC-specific improvements. This remastered trilogy will offer a modernized PC experience across all three games with native controller and 21:9 widescreen support. Furthermore, there will be user interface navigation improvements, and DirectX 11 compatibility.
— Mass Effect (@masseffect) February 3, 2021