Silent Cartographer alone has more variety than the entirety of Destiny. Same for Halo, AotCR and Two Betrayals. Destiny doesn't even have one vehicle for multiple players, like the Warthog or the Scorpion, or a flying vehicle, like the Banshee.
The encounters were also more diverse and had better flow in Halo, with cool mechanics, like the classic plasma weapon to remove shields + headshot, or the shoot fleeing grunt in the back + headshot. The most interesting mechanic present in Destiny is stunning those cabal with shields and follow with a headshot, which is basically another version of the classic jackal stun + headshot. Halo also didn't have awful bullet sponge enemies like Destiny does. The fact that you could pick up weapons on the fly also helped make the encounters more dynamic and interesting. And that's without mentioning the vehicle battles, which are almost non-existent in Destiny, sadly.
The weapons also managed to feel more diverse, with cool alien weapons like the plasma pistol and the needler. Destiny only has 9 weapon types, and none of them is especially interesting. Only the fusion rifle kind of tries to be somewhat original, all the other are just variations of the standard weapons present in pretty much every FPS (pistols, machine guns, rifles and rocket launchers)
And that's just Halo CE. If you also consider the sequels, the comparison is even less favorable for Destiny. Gameplay mechanics like vehicle boarding, flood resucitating corpses, or using the plasma pistol EMP to disable vehicles. Weapons like the gravity hammer, the energy sword, the spartan laser, the brute shot or the grenade launcher. Vehicles like the wraith, the brute chopper, the hornet, the falcon or the revenant. And what about levels like Delta Halo, Tsavo Highway, The Storm, The Ark or The Covenant, all of them also better designed and more varied than anything you can find in Destiny. Or features like theater mode, firefight, and forge? Destiny doesn't even give you the option to play custom games or split screen co-op/MP (both of which were already included in Halo CE, thirteen years ago) or choose what gameplay modifiers (skulls) you want when replaying levels, or play strikes alone (unless you are playing the weekly, you are always forced into matchmaking)
What was Bungie thinking? IDK, but I'm glad the critics are being "harsh" on Destiny. Hopefully they will get back on track with Destiny 2, because this game is lacking in so many aspects it's not even funny. I expect much better from Bungie.