(disclaimer: the items are no longer actually called 'keys', though all your keys were converted into whatever the hell they are.)
I feel like the most important part for someone who quit due to the abysmally miserable void drop pools is that, if you're in a party all looking for the same thing you get four chances because each person who brought a 'key' gets to roll on the table, and everyone gets to choose which of the drops they want. (And to be clear, you can all choose the same thing). If you choose someone else's drop (for example, when literally everybody still rolls orthos prime handles grumble grumble) that person gets a few bonus Void Fissures.
Void Fissures drop from the enemies you fight while activating the void tear, and can be used to upgrade your 'keys' and shift the drop chances towards the rare end of the pool, which I assume is practical if you only have a few of that key and want to maximize your chances.
I'm not sure how easy it is to get keys - presumably just like old times, so 'sorta grindy' - but overall the new system is a massive improvement. My buddy literally bought plat when it was on sale so he could buy Nova Prime Systems - which could only be obtained by a grueling 20 minute grind of garbage-tier infested in the Orokin Derelicts at a drop chance of 'fuck you'%, with the other stuff in the drop pool being not-Prime-parts meaning you weren't even getting ducats for doing the missions.
We got it while we were going for something else in the hour and a half we played last night, though that was admittedly because it was a common drop in the same pool as one of the Mag Prime parts. The worst situation you can find yourself in now is needing something rare from a high-tier key, but that's infinitely better than anything in the Derelict, and uproariously better than most of the Void Missions. If I never do Void Survival for 20 minutes again, it will be too soon.
It's worth noting that as of last night Sorties appear to literally be broken, and nullifiers were allegedly tidied up to have more consistent effects, but the real takeaway is they now pop Frost's bubble if they touch it so have fun doing high-level anything-you-need-to-defend! (And no, Excavators still do not scale).