The only $100+ million dollar game I know of was SWTOR, that is neither here nor their, just saying.
I would personally make a ridiculously epic overly funded out the ass (if you don't mind me saying) Star Wars Battlefront 3, but with a major twist, it would be PC only and the battles would be like nothing you have ever seen. You would only play as hero classes, commanders, bounty hunters, Jedi, Dark Jedi, Sith. All piloting, shooting and lightsaber/force combat would be player skill based, I would make lightsaber/force combat much like Jedi Academy (but with major tweaks & far more advanced).
Jedi can block in all directions, a small warning(window) would warn you of a incoming attack (saber, blaster bolt, grenade etc). You have a small window for holding block, you cannot hold down block, it would be a parry system for all incoming attacks. How it works is, if their is multiple blaster fire coming at your Jedi you could block 3 shots at the same time if you block within the window. This window would be very small, we are talking a twitched based class. This is not Assassins Creed 3 mechanic. You would need a low input lag display, a fast computer to be remotely good at a Jedi, otherwise a player with a carbine would mow you down.
However if you were a twitch based player (good with a keyboard or controller or fight stick) it would be a very rewarding badass feeling of playing as a Jedi in a very huge open battle. We are talking about a $100 million dollar budget and a PC only game with 0 mainstream market, that means the game is not out to please anyone other then mid to high end PC's. The games scale would be massive, battlefields would be inbetween a Arma II & Battlefield 2, smaller then Arma II of course (that is a huge open game). So their would be space battles and ground battles, a lot of ground battles would invovle space battles as well.
It basically would be Star Wars Battlefront with 10x the size of battle maps, insanely fliud combat, a heavily tweaked advanced Tie Fighter like space combat. The sounds for weapons, blasters, sabers, starships would be incredible, having a Soundcard with 5.1 with base would be amazing or headphones. The money involved in the sound of the game alone would be quite a large sum.
The jet pack mechanics would be skill based, you could kill yourself in a hurry if you didn't know what you were doing (like flying a helicopter in Battlefield 2 or 3). The most hardcoe element about the game would be Jedi, however a Jedi could die in a fighter just as easy as any class etc. Their would be no force warnings for that just to balance the game and give all players the choice to become Jedi. Jedi mechanics again would be similar to Jedi Academy however the most innovated thing about the entire game would be the parry system for Jedi.
The battles again would be much larger in scale, size, and player population then Battlefront, the game would be very optimized with the latest technology but also require mid - high end PC's for the scale of the battles. Star Destroyers etc are all controllable by any player, their would be a lot of interior roamable space & NPC population within a Star Destroyer for what kind of game it is, however given the size of the battles only one player could control a ship like that. The Star Destroyer class/type of ships would be command based, which means you target, issue fire etc.
Everything else is up to anyone's imagination, I mean this game hands down would have a recommended requirement in a brief nuttshell:
8G DDR 1600, quad core 3.0 (default clock), GTX 550 TI or above. If you ran anything past 2x AA you would need 284+ bit memory interface along with a very min of 2G DDR5. If your running dual link 2xxx x resolutions on 27"+ displays you'd absolulty need a 384 bit memory interface card with 4G DDR5 (current clock speed wise cards like a 680 etc)
Again recommended requirements, and that is if the game was out right now, even with the recommended requirments you would haft to lower the settings a fair amount. The technology & optimization of the game would be very advanced but because of the very large epic scale of the game however it would be taxing to achieve what the game is going for. The game is only marketing to one fan base, it would motivate people who did not have a PC to buy one, they'd figure something out

However, funny as all this, their is not one thing I listed that innovated aside from it being a large scale advanced Battlefront game with ground to space epic scale battles.
The real innovation would be in the lightsaber mechanics, the parry system, it would not be a timed counter system, but a timed parry system. Which means, if it says "incoming attack" after you hit parry, the parry holds a very breif amount of time, along enough to deflect 3 to 5 blaster bolts within one single parry. I would compare the timing to Street Fighter 3rd Strike. The Jedi would have good mobility via force power, saber attacks via Jedi Academy, innovated twitch based parry system.
You could play as or get into about any vehicle a Star Wars fan could dream of. The game would succeed because it has already been funded for development and release, the game would be so epic for what it is that it would make fans build mid to high end PC's. They would sell their $1000 TV's and buy a PC with a 24" - 27" monitor.
That's about it, what would you guy's do?