What are you going to do? Easy. You check out this rundown of awesome game features that absolutely definitely *have* to be in the sequel. It's an essential laundry list for imaginary game developers everywhere...
Never mind that players only made use of one of the 200 available weapons when they rattled through the first game. If the sequel doesn't contain at least 20% more things that kill and go bang then it has failed and will be ridiculed. Chainsaws, flamethrowers, and grenade variants (like sticky grenades and pipe bombs) all make really good sequel weapons. Oh yeah, and shields. Shields are always a good bet for sequels.
Whoever heard of a sequel with a fully-realised organic sandbox open world that's half the size of the original? No one. Because it doesn't happen.
Players like making hideous looking characters with pink afros and magnetically opposed eyeballs. So if it didn't make the first game, be sure to throw customization into the mixer. And if it did make the first game, just give players the option to customize the shit out of everything else. Rooms. Armour. Vehicles. Everything.
Something that is 'overhauled'
It doesn't matter what. Combat system, physics, front-end interface, mip-mapping transponderating flim-flam... whatever. As long as the press-release or back-of-the-box mentions that *something* has been 'overhauled', 'rebuilt from the ground up' or 'completely reworked', you can make some ambiguous claim that the action has been 'taken to the next level' or is 'even more intense'. Gamers will subconsciously play the game thinking that something drastic has changed. And no-one will remember what the 'overhauled' thing was like in the first place anyway.
Above: Totally 100% better than the first game
Next: More stuff to shove in the sequel...