So what are the HM differences?
http://www.reddit.com/r/DestinyTheGame/comments/2t6u0v/crotas_end_hard_mode_megathread_12115/
General
All enemies are 33.
No revives
Primary Weapons drops at all major sections. (Abyss, Bridge, and Crota)
Enemies appear to take less flinch damage
The Abyss
Chest is only a single drop
Weight of Darkness increases quicker
Ogres, Cursed Thralls, and Knights are now Majors (Yellow bar).
Oversoul Edict is a confirmed drop for this section
The Bridge
No Major differences
The Abyss Defiant is a confirmed drop
The Tunnel
3 Shriekers are now here
Shriekers will respawn
Deathsinger
Liturgy of Ruin will now activate sooner
Only has one reward
Crota
Chalice does not spawn
Hallowed Wizards will now spawn to the left of Crota
Gatekeepers have been added to the Crota fight
Boomer Knights and all Knights in Crota are Majors.
Gatekeeper does not need to be down to strike Crota.
Gatekeeper will despawn after Swordbearer is dead
New shader is called Glowhoo and looks like this: Preview, in-game screenshot
Fang of Ir Yût is a confirmed drop for this section
Word of Crota is a confirmed drop for this section