For me, mirroring what other have said, simplicity is key. I don't care about tonnes of weapon customization, definitely don't want wall running and all that. Just a clean, simple game as we saw from CoD4 through to the Black Ops days.
In terms of matchmaking, SBMM has really ruined the multiplayer experience for me. I feel like as with other multiplayer games there should just be both a ranked and unranked playlist to let players decide which they want. At the very least, if SBMM is necessary, there could be better transparency so you have some way of indicating how good you actually are at the game! I don't see the point in multiplayer as is, I need a goal to work towards whilst playing!
I've really enjoyed Warzone over lockdown, but again would love a barebones version without loadouts, having to rely on finding weapons/attachments etc.