Mass Effect 1 style, absolutely.
A huge part of the series was lost after the removal of the Mako IMO. Sure the thing could've controlled better, sure the planets could've had more than like 3 kinds of objectives, but it has so much potential. What the uncharted planets brought to ME has never been replaced after their removal. That sense of exploration, that sense of isolation, that sense of vastness; all of these were essential to what the Mass Effect 1 experience was as a whole. They were the ultimate opposites of locations like the Citadel and the clubs you'd visit. They weren't perfect, but it should've been the first step.
To improve them, there simply needs to be more variety. Terrain generating system and like 20 different skyboxes that can be manipulated in all sorts of ways from color to major natural satellite locations, to the number and location of suns, and day or night time settings. Then you can layer a weather system on top of that with different levels of rain, different scale hurricanes, sandstorms, incredible heat, sub-zero cold, different levels of snow, ash in the air from continuous volcanic activity, stable weather, etc. This could make it easier to create unique planets with a variety of looks and sounds without having to meticulously hand craft every single uncharted world, especially since major plot and side mission important locations will be receiving the majority of those manhours.
The next step would be the activities on the uncharted worlds. This I think should be more random for each playthrough. Have many different different kinds of relatively small activities made- resource gathering, artifact locations, saving stranded travelers sending out an SOS, fighting off raiders from a small base, ambushes, major alien creature attacks (like the Thresher Maw), etc.- none of which would be explicitly chosen by Bioware but assigned randomly for each player during each playthrough after the planet is scanned for activity. So while the worlds are the same for each player, activities could be vastly different from a combination of small menial tasks, to a search and rescue interrupted by an enemy raid, to a enemy raid interrupted by a creature attack, to a creature attack interrupted by a second creature attack, to a simple defunct laboratory or derelict ship with nothing in it but a still functioning beacon for help that nobody received in time. The only developer's touch you feel here is them making sure all the systems work together correctly. Aside from that, many things could happen, some things could happen, nothing could happen. Unpredictability and chaos, thus is the nature of space.
Through all this the Mako should be present and become its own character again and that electronic ambient score should come back in full force adding to the atmosphere. Uncharted worlds should totally still be "third their" missions in regards to plot importance, but they should be not be treated like or thought as filler. They can provide an important mood to the title simply impossible to achieve in high traffic areas, and beautiful/hostile visuals, both of which can give the universe itself it's own personality. It can make the player feel small and insignificant. Not everything is made and scripted for us, and not everything is in our control.