Raid Composition

This is an encounter that, at least for first kills, will require absolute min-maxing of raid composition.
2 Tanks
7-8 Healers
15-16 DPS (No more than 5 melee due to soaking requirements for Meteor Slash. At least one hunter.)

Raid Composition Commentary

Tanks: Can be either protection warriors or feral druids; a feral druid can help to boost damage with Faerie Fire and Mangle if one is not already included with the melee.

Healers: 2 Shaman, 2 priests, 2-3 paladins and 1 druid. Priests and 1-2 of the Paladins heal the main tanks; maintaining Inspiration on the main tank is necessary at all times. Shaman heal the damage the raid takes from Meteor Slash. The druid and 1 paladin should heal Burn targets.

DPS: Limit to 5 melee DPS. Warlocks can prove very useful in numbers here and stacking for absolute maximum DPS will be needed. Limit yourself to 1-2 Shadow priests; healers on the tank will need one due to Brutallus' damage output and spike capability.

Buffs and Consumables

All raid members must be fully buffed with flasks, elixirs, food, Haste Potions, Destruction Potions, and Ironshield Potions. Melee DPS classes should use old world Elixirs of Demonslaying. Drums of Battle are very useful and any raid members who can should be using them. All of these should be used on cooldown and a Heroism rotation should be developed and used. The raid must put out 27,777 DPS to beat the enrage timer.

Brutallus

10,000,000 Health, Demon, Taunt-able, 6 minute enrage timer. Brutallus himself has only a few abilities.

Sunwell Radiance
Chance to hit increased by 5%.
Enemy chance to dodge reduced by 20%.
This buff is currently active on all NPCs in Sunwell Plateau, including bosses, it seems intended to balance encounters against high avoidance tank gear. It also makes the rogue ability Evasion less effective. It does not require any particular raid strategy to counter, but tanks and rogues should be aware of it. 

Meteor Slash

This is a 30 yard range fire based frontal cone attack. It has a 1 second cast time and a 12 second cooldown. It deals 20000 damage split between all targets within the cone, and applies a stacking debuff that increases fire damage by 75%. It lasts for 40 seconds. This cannot be resisted, dodged, parried or miss.

Burn

A fire based damage over time attack. At any point during the duration of the debuff, if the afflicted player moves within 2-3 yards of another player, they will spread a fresh debuff to the new player. Burn is randomly targeted. Damage starts at negligible amounts and increases every few ticks, culminating with a ~6000 tick at the end. The debuff lasts 60 seconds, can be resisted, and is removed by Cloak of Shadows, Iceblock, and Divine Shield.

Stomp

This reduces the armor of Brutallus' primary target by 50% for 10 seconds and also deals 18850-21150 physical damage after mitigation. It will hit a well geared tank for approximately 5000. Note that this attack removes the Burn debuff.

Melee

Brutallus has a very fast attack speed and hits off hand and main hand. Without Stomp, his main hand will hit for 6-8000 and his off hand will hit for ~3000. During a Stomp they will increase to 8-11000 and 4-5000 respectively.

Enrage

After 6 minutes Brutallus will gain a 500% increase to his damage and 150% increased attack speed. This will kill even Shield Wall-ed tanks.