Genuine questions: What does Starfield do to innovate? Are there mechanics, narrative twists (no spoilers), or features moving the industry forward in a new direction? What's here that I haven't played before?
Worse mechanics than games that are dedicated to each function.
Ship building is janky, it doesn't actually make any kind of difference, and there are other games with better, cooler customization that allow you to do more granular things. The ship stats don't actually matter, because you can carry your crew of flunkies around the galaxy with any kind of setup, regardless of the actual stated crew stations and passenger capacity. Fuel exists but is inconsequential, it's a number that goes up and down as you travel independent of your interaction with it. Space Engineers and Empyrion Galactic Survival are two games off the top of my head that kick the shit out of Starfield's ship building and exploring.
I feel like the gunplay is worse than it was in Fallout 4. That might not be because of how the guns fire so much as it's probably directly related to how much everything is a pointless bullet sponge. You can have a pimped out Orion and shit still takes a bunch of hits to go down, and they're all the same sets of enemies: renegade spacers in random mines and outposts.
The only new thing on top of all the mechanics culminating from Skyrim through Fallout 76 that they added was a research system, which is perfunctory at best and super annoying and artificially limiting at worse.
So to answer your question? Nothing. There's nothing they improve upon that hasn't been done elsewhere - the gimmick functionally just is that all these elements exist in the same game in a very disjointed fashion.
Personally I really hate when you fight the same generic enemies but they just get bigger numbers to become bullet sponges. A lot of games that want to be "endless" do this, e.g. Warframe. At least make the tougher baddies bigger? Give them cooler armor or something? Don't make them look identical to the level 1 grunt.
Supposedly No Man's Sky was the vanguard of procgen but I wasn't impressed. I get the impression that Starfield uses it very similarly.
For characters and ships, all NMS seems to do is combine permutations of prebuilt parts, not create any actual unique parts. Spore was way more impressive a decade and a half earlier because it tried to animate whatever wacky creature the player designed.
For terrain, NMS doesn't even create biomes. You won't find a river, glacier, waterfall, or oasis anywhere. They didn't even apply the system to space stations, those are identical everywhere in the universe. Valheim and even Minecraft did better.
Starfield's biome and planet generation is extremely barebones, but placing that in a single player RPG with the radiant quest systems is fairly innovative. Imagine STALKER Anomaly style tasks, but with proc-gen landscapes.
This combo allows any character to have more content available to suit that character style far more than Skyrim or Fallout 4 style faction radiant quests.
Still needs far more work though, it's half-baked.
Starfield's biome and planet generation is extremely barebones, but placing that in a single player RPG with the radiant quest systems is fairly innovative. Imagine STALKER Anomaly style tasks, but with proc-gen landscapes.
This combo allows any character to have more content available to suit that character style far more than Skyrim or Fallout 4 style faction radiant quests.
Still needs far more work though, it's half-baked.