Well screenshots have been leaked of this very early build of Halo:Reach beta and according to neogaf here are some details:
Gameplay Details:
Campaign
Elites – Better than monkeys!
Privacy – potential drop in, drop out co-op multiplayer
Weapons:
New Needler-based Heavy Weapon – Looks like a Covenant version of the Spartan Laser!
BR – It’s back with a new look!
AR – Same old, MLG favourite!
Needler – Now with more pink!
Laser – Red eye again!
And the bottom details are just speculation
New Carbine
new carbine that shoots needles, and explodes when 3 needles are hit
BR
it is a one shot battle rifle with 12 rounds, pretty powerful and effective long range.
Perks
This is what the HUD looks like. In the bottom left, you can see your squadmates health and names.
Right above the radar shows what perks you are carrying. When I played there were 3 perks-sprinting, cloaking, and halogram.
The sprinting makes you run when you hold LB,
cloaking makes you invisible (when you cloak your radar jams and you can’t really hear anything around you).
The halogram creates a hologram of yourself, so enemies will shoot at both.
