Like many said in a topic about the worst raid to the date, and I agree, the Dragon Soul was Blizz' failure. I expected much of the raid, and I'm still sure, that it did have potential to be epic! Firstly, I'll point out what I consider to be the drawbacks, and then I'll present things that coulde've been added.

1. Morchock. The first boss is ok. A "siege weapon" we are to destroy before he tears down the WT. Nothing to add.

2. Zon'Ozz and Yor'Sahj the Unsleeping. Bosses themselves are satisfying, BUT - they are the commanders of an attacking army! So, we are to tear the
the invading enemies, or better than that, evade huge masses of foes, for they'd outnumber the raiders, but there must be dozens of cultists, both melee zealots, blinded and zombified by their sect masters, and mages too, faceless ones, elementals, twilight drakes howering above...all that masses going wave by wave to the tower...and we should follow a narrow path, evade huge packs of mobs, quickly kill them before they attract more...and only then reach the command posts and slay the generals.
3. Twilight Father - I was really disappointed to only see him in a 5-man....was the first serious disappointment about the raid. This is against the logic - Benedictus became the same rank that of Cho'Gall; we fight his underling Hagara in 25 mode, and the head of the cult - in 5 man?? And more to say - he has his own history of a downfall, he participated greatly in the Cataclysm events - that is unfair to leave him at such a minuscle event... I have my own idea for the fight, but that's a bit later.
4. Deathwing. The single person that could've make epicness and failed to do. The main reason for me is - WHY is the only abilities he did were just some pieces of s*it falling off him and biting us??? Is that a combat tactics of a strongest creature on Azeroth??? To stupidly stare at his enemies, have them bleed him and make his blood bite them? Is that all he has, except for the single meteor? It is meant that he is a sort of a weapon of mass destruction - then show us!!! That was exactly what I expected too see since the beginning of Cata - to see DW in action, see him ripping geysers of magma, shaking the earth and covering all in molten flame, crushing with magic and twisting with curses....Yet, we were deprived of it. We were only allowed to cut off several tentacles and puhch his head while he was knocked out...I see this the main reason for DS being estimated the worth raid - we received MUCH less than we expected.

So, my ideas.

1. Not 2, but 3 fights with DW!
The first one being the fifth encounter, right after Hagara, and called, say, Assault of Deathwing.
So, when we teleport away from Nexus, something appears to go wrong. Instead of teleporting right to Wyrmrest Temple as was planned, we are cast somewhere in the Dragonblight, outside the Temple.
When the encounter begins by speaking with Nozdormu, a portal opens and Deathwing in his human form appears. He has 858 million hp, and besides a buff "Elementium Armor" that decreases damage dome to him by 80%. So, its actually a cat playing with mice more than a fight.
During the first phase he wields a fiery mace, uses mostly fire and earth magic, and our purpose is to take him to 95%. Then, Nozdormu casts a bolt of energy at DW, he drops his mace, and the tank clicks it to land a swing at DW, weakening his armor.
As with a fight with Alextrasza, he falls on a knee and sprouts tentackles from his back. In phase 2 he uses earth and shadow magic. Here we are to take down 10 more % of his health to push him to the last phase. At 85% he gets angry and begins to transform into dragon. We are to flee (a path opens), because when he finishes transformation, he casts a flame wave and instakill those to slow and lift into air.
The third phase actually is similar in structure to Escape from Arthas in HoR, but much harder. We are to get to the safety of the WT, while DW chases us. He has 2 subphases - air, when he breathes fire, impeding the path, ripping open fissures that throw lava bombs, fires magical balls of massive pressuse, impaling with earth spikes, and so on (think, what could you add to that), killing nearby cultists in process; and land phase, when he lands and channels a huge, instance - wide earthquake that deals damage, occasionally knoks down and making randow explosions that toss players around.
Finally, when we reach the gates of the Wyrmrest, last wave of adds comes and DW begins to fly in a circular shape, raining fire balls all over the groung, and making the flames move, burning us and and adds alike. When all adds are dead, we are to run to the "safety" of the Temple, where Benedictus in his bishop disguise meets us...

2. The Twilight Father.
This is a complicated 4-phase fight, that also symbolically represents Benedictus' gradual downfall from almost a holy life to the abyss of madness.
In phase 1 he fights in his priest form. Phase lasts from 100 to 80 % health, so its a quisk and simple dps check. He summons columns of light that increase damage taken, summons balls of blinding light and attampts to heal himself, which must be interrupted.
In phase 2 he turns into his true form - Twilight Father. This lasts from 80 to 40% hp. He uses powerful shadow spells like - channeling 3 orbs that are to be damaged before they are launched, or they inflict too much damage in a lagre AoE and leave a void zone, hurking volleys of twilight spikes that leave shards of twilight that corupt us from within, resonating with any damage received, casting debuff that applies a stack of dot whenever a player performs any cation, an sooo on.
In phase 3 he teleports to the centre of the room and pulls himself and the raid into the realm of twilight. He takes only 50% damage there, and the phase lasts from 40 to 25%. In this phase he summons adds, like faceless ones, channels twilight, maybe even uses a sort of twilight lightning, think of Palpatine.....
Finally, in phase 4, he sucks the surrounding twilight into himself, transforming by half into a faceless one. This is a burn phase - he grips players with tentacles, sucks health from players, fires beams that decrease our demage and gealing dealt, so its just a very harhs dps race, phases 2 and 3 being battles for survival.

3. Madness of Deathwing.
We can make him busy in phase one by adding such mechanic - he chooses an Aspect and breathes at him\her, and Aspect fires his breath as well. We are to support Aspect, think of Sinestra's phase 2 with Calen.
In heroic mode, killing limb tentacles removes not 20, but only 10% of his health. So, we begin phase 2 at 60% and finish it at 40%, where the real challenge begins. Here, in a heroic only phase, Deathwing breaks the isles we fought on, and the Aspects grand us blessings, turning into drakes of respective dragonflights, think of Malygos, phase 3.
The phase revolves around 2 main mechanics. DW has some regular weapon, say fireballs and somethig else, and unique powerful attacks, that can be countered by respective Aspects, but wouls drain the Aspect out of much power.
Secondly, it's a Dragon Soul mechanic - we must not only dps DW, but also make Aspects channel power to charge the DS. We are to find balance between channeling power into DS and dpsing the boss, for if we charge too much of our power, he'll wipe us with special attacks, and if we spend too much to block his spells, he won't have enough charge.
After the timer expires, he begins to cast the Cataclysm one last time. We cannot damage him below 5%, so we must charge the DS and order Thrall to fire it. If we didn's dps him enough or don't have sufficient charge in the DS, he casts the Cataclysm and wipes Azeroth. If we have enough charge in DS, the fight is won, and he explodes harmlessly, leaving only a jaw behind.
Do you like the ideas?
What would you add to these encounters?
Would you call DS a good, epic raid if it'd look like this?