I haven't finished it yet, primarily because I keep telling myself that I WILL do all of the side quests, etc. Unfortunately, exploring the planets and doing the side quests tends to be very boring. I estimate that I'm about 1/3 - 1/2 of the way through the main story. I should just reinstall it and finish.
It's not a bad game, but it's not one of my favorites (that may change when I finish the main story). Like many others, my primary complaints are combat (awkward and somewhat mindless), the inventory system (needs better organization, and I wish there were more weapons and more weapon mods, or some sort of crafting / combining items to get a weapon that suits your needs), and the side quests. There's plenty of plants and galaxies that you can "visit," but only a few can be explored. Even the ones that you can actually land on and explore tend to be the same thing over and over - a crashed satellite that requires science / whatever skill to retrieve, a few small buildings with a data disk or something of that sort, and a big building that you can enter and fight enemies in. I've found a few good weapons on explorable planets and several items for side quests, but nothing that really makes me want to stop at every planet I look at.