Plumber is in the first level
Harder difficulties make enemies react faster, move faster, shoot more accurately, deal more damage and gives them more HP, rather than JUST the latter 2 like in aCiT. (YESSS) And just from watching around 21:55, the enemies do seem pretty relentless (The guy is playing on the hardest difficulty)
There are areas that you can skip and come back to, and there are completely optional areas as well.
Some wide open areas, and some more linear areas with branching paths exist. (I'm guessing they tried to balance them well)
The developers sat down and played through some of the older Ratchet games and pulled their favorite moments from them and.... (The guy kind of goes off track from there but I'm guessing they used a lot of those moments as inspiration)
There is no Thruster Pack, but one of the screenshots shows something that resemble one. He said it functions more like a jetpack.
Tachyon and the Cragmites will be mentioned somewhere in the game's story.
Control scheme is sort of a hybrid between all the Ratchet games. There is no auto aim like in the older ones. You aim where the screen is facing as opposed to other Ratchet games where you aim where Ratchet is facing.
There is a lock strafe mode.
They tried to copy the wrench slam from the PS2 games to get the exact same feel. They mentioned that in the PS2 games, the wrench kind of extended and the head got bigger before it slammed down. (Im not sure if it was like that in the other PS3 titles)
They don't know if there will be a demo at this time.
Hoverboots are somewhere in the game and you need to be skillful enough to get them.
Raritanium upgrade system is included. Similar to the one in ToD (Seemed more fleshed out)
You can try weapons before you buy them (Like in UYA) Showed off in the video at 37:15
Shows many different paths on the map of planet Yerek (38:35)
Temporal Repulser is OP
You can switch back to previous armors (you couldn't do that in any other R&C game)
Someone asked on the stream if this would be the hardest Ratchet game ever. The dev said that there is a very difficult mode (I'm guessing it's a difficulty you unlock after beating the game) that he even still has trouble with. (It does look like it has the potential to me much more difficult than ToD & aCiT on the harder difficulties just from watching the AI from the first level on Legendary difficulty)
Not enough Raritanium in the game to fully level up all of your weapons on the first playthrough (there is also the traditional weapon XP system just in case you were wondering)
There are infobots like in R&C 1
Can see 2D Clank section at 54:00
They have a lot of references to the older games that fans who have played the other R&C games may catch.