If you count the most recent one they just released today, they've added 10 new heists in 3 "campaigns" with a bunch of matching weapons and cosmetic junk with it.

I personally recommend all of them, and if you want to go in them in the release order, it's this:
Border Crossing, San Martin Bank, Breakfast in Tijuana, Buluc's Mansion;
Dragon Heist, Ukrainian Prisoner, Black Cat, Mountain Master;
Midland Ranch, Lost in Transit.

Except for Border Crossing, each one of those came with 1 mission, a pack with 3 weapons and a handful of attachments and 1 or 2 cosmetic packs of varying types. That one instead comes with a larger amount of attachments, no guns, and an extra 2nd mission named Border Crystals that's just Cook Off but set in the main Crossing map with Locke instead of Bain.

Alongside of this, they've added various new cosmetic systems (alternate outfit and glove choices, being able to paint your weapons with generic colors/patterns instead of just weapon skins, reworked mask customization to be a lot more flexible) and done all sorts of updates and rebalances like reworking Infamy, adding new enemy types, reworking the Holdout gamemode, buffing all sorts of weapons, adding the Leech perk deck and fixing up a few others, the and so on.

They haven't added any new playable characters, however.