Here is what it is like:
Taken king: Nice but meh just another set of perks on your character, not as we hoped.
Rise of Iron: Adds unique artifacts with special perks that help change gameplay related to the Iron Lords.
Moments of Triumpgh: Adds new artifacts that drop from the updated raids, but don't offer any speical perks like in Rise of Iron.
Destiny 2: Removes them like they are not there.
I personally loved them cause it freed me to run third eye without Knucklehead Radar it even on a titan. Would love to run a different exotic. I doubt they’ll come back though.