*The Ghost/Sea Witch could possibly have been a minor entity in the Maelstrom, but it could also be attached to Queen Azshara. It is pure speculation whether it is or not.
Between where Matthew Rossi left off and I pick up, Thrall and the Orcs didn't do anything particularly exciting. Gathering the scattered tribes and clans of the Horde isn't small potatoes, but it's also not interesting, so let's stop talking about it. After all of that was done, Thrall was camping with a small group of the New Horde when he received a vision. A vision of fire and brimstone raining down from the sky, and a brutal, bloody battle. Coming to the conclusion that he should learn more about this vision, he eventually met a mysterious prophet, who we know as Medivh. Medivh appeared to a few others as well, such as the King of Lordaeron and Archmage Antonidas of Dalaran (and Jaina Proudmoore by proxy). Thrall and Jaina were the only two to trust this Prophet, which most people find to be an admirable part of their personalities, but I say they're utterly insane to throw caution to the wind and listen to the advice of a talking raven. Whether it was sane to do so or not, they listened to the prophet.
Thrall was told to head west, across the ocean to Kalimdor. He gathered up his green-skinned friends, stopped by a Human settlement to free Grom Hellscream who has a thing for getting himself into trouble, then Grom had the idea to steal the Humans' ships to sail to Kalimdor. What's stealing a few ships after a long, bloody holocaust against the Humans followed by a few years of Orc enslavement? No big thing, really.
It wouldn't be Fantasy without something horrible happening on their journey, so naturally, Thrall and a few of the other ships found themselves amidst a mighty storm near the Maelstrom. Grom and many others don't seem to have met the same fate. Thrall and his companions sought shelter on a nearby island, only to discover that some pretty bad stuff was going down. The Darkspear Tribe of Trolls were besieged by two separate forces, Murlocs and Humans. It turns out, the two of them weren't specifically after the Darkspear. The Murlocs were using the Darkspear as sacrifices to... well, someone*, and the Humans were there to keep the Murlocs away from Human settlements. They weren't there to attack the Trolls at all. It was, most likely, miscommunication on both sides. Of course, Thrall only discovered this after busting Human skulls in an (failed) attempt to protect the Horde and the Trolls.
That Orc/Human conflict was actually exactly what the Murlocs needed to find their opening. The fishmen attacked with little opposition due to the Orcs, Humans, and most of the Trolls preoccupied with each other. Thrall and Sen'jin, leader of the Darkspear, were both taken captive to be sacrifices. Thrall was able to break out of his cell, but wasn't able to save Sen'jin, who had been taken as the Murlocs' first sacrifice. As Thrall tends to do, he wrecked up the place and killed the Murlocs en masse, and rightfully so. The entity the murlocs were worshiping, a Sea Witch, appeared to Thrall and laid a curse upon him, that he and his men would be swallowed up by the sea. If you hadn't guessed, no, the sea did not eat him, though they did pretty much hit Kalimdor head on and shipwreck on the coastline. That's almost the same thing, except... you know, not at all the same thing.
Oh yeah, the remnants of the Darkspear Tribe joined the Horde. Yaayyy!
Thrall and his crew were still separated from Grom and the Gang upon reaching Kalimdor. Thrall's timing was, as always, impeccable. Not long after his arrival on the continent, he witnessed a battle between two factions, down from the previous three. The centaur and tauren were going head to head, and it seemed the centaur were winning. Until, of course, Thrall and his Horde decided to jump in. Grateful, the tauren chieftain Cairne Bloodhoof volunteered to help the Orcs find their destiny. Then Thrall informed the chieftain that the centaur were heading right for Cairne's village, so that had to be put on hold for awhile.
After killing a metric crapton (best system of measurement ever) of centaur and escorting horrifyingly slow kodos all over Kalimdor, Cairne showed Thrall the location of the Oracle that would help the Orcs find their destiny. Thrall sought out this Oracle, which happened to be in Stonetalon Peak, and was shocked to find Grom Hellscream battling a group of Humans under Jaina Proudmoore's command. Thrall, really? Are you really still surprised when Grom Hellscream attacks something?
Thrall stopped the battle, and decided it would be easy to bypass the Human territory in Stonetalon Peak by renting Goblin zeppelins to carry them up the mountains. Thrall and a handful of other Orcs moved quickly and quietly toward the Goblins to make their purchase. And then they were attacked by Humans in retaliation for Grom and the Warsong attacking them. Again. Thrall made it out alright, stopped to kill some extra Humans to keep them at bay, and then got his zeppelins. He made Grom stay put in Ashenvale so he didn't wreck up the place when Thrall met the Oracle.
The Oracle was none other than Medivh, who convinced Thrall and Jaina that the Orcs and Humans would need to work together to defeat the horrors coming their way. The two accepted, but were hesitant. Medivh also informed Thrall of another small issue: Grom drank the blood of Mannoroth. If you haven't been keeping count, that's the second time he willingly drank the blood of demons for power. Luckily, the combined forces of Thrall and Jaina managed to purge the taint from his body, more or less. It took Grom's famous slaying of Mannoroth shortly afterwards to finish the job.
Again Medivh appeared to Thrall and Jaina, this time with Tyrande and Malfurion in attendance as well. The Night Elves joined the temporary alliance to stop the Legion as well. Their forces gathered on Mount Hyjal, where they would make their stand. Thrall and Jaina's forces fought against Archimonde and the Legion at the base of the mountain, to buy Malfurion enough time to do what Night Elves do best. Blow up something really, really big. Gnomes? Goblins? Pfft. It's all about Elven explosions.
It was there that the Night Elves parted from the brief alliance. Thrall and Jaina have since attempted to keep their alliance strong, but their people are not so keen on the idea. While the two of them get along to this day... well, old hatreds die hard. Most of the Orcs still hate Humans and vice versa. Jaina also only speaks for herself and those that serve her, and not all Humans everywhere.
Her own father decided to make this quite clear. During the founding of Orgrimmar in Durotar, the former named for Orgrim Doomhammer and the latter named for Durotan, Admiral Proudmoore decided he didn't want to let the Orcs get a foothold in Kalimdor. It certainly wasn't an unfounded fear, either. The Orcs did, technically, sink half of his fleet and get his son killed. That would pretty much piss off anybody. His offensive on Durotar didn't do much to calm the old Admiral, because Jaina helped Thrall and Rexxar, the new Champion of the Horde, kill Papa Proudmoore. Demonize the man all you'd like, but his son was killed, he wanted vengeance, and then his daughter basically killed him, though it was at Rexxar's hands that he died. That's pretty messed up!
Things were relatively calm for a few years after that. As calm as Azeroth gets, anyway. There were many incidents between the Horde of Orgimmar and the Humans of Theramore that jeopardized their rough, uneasy alliance, including an incident with the Burning Blade. It can be assumed that Thrall and Jaina are still on good terms, and Theramore does not outright hate Orgrimmar and vice versa, but game mechanics in WoW make this quite difficult to properly represent, so they are allied to their primary factions only.
In more recent times, Thrall has learned quite a bit more about his heritage, not to mention his legacy as a Hero of the Horde has begun. The settlement of Thrallmar has been built on Draenor, and in the Horde, you know you've made it when they name something after you. They still have things named after Kargath Bladefist, and they kill that guy.
Thrall has paid a visit to Outland to meet the mother of Durotan and his grandmother, Greatmother Geyah. Despite not being born there, or ever having seen the place previously, Thrall announces the Mag'har settlement in Nagrand his home. I'll forgive him, considering it is a large part of his culture. During his visit to Nagrand, Greatmother Geyah tells him something precious: his 'real' name. Thrall was to be named Go'el, meaning 'to redeem.'
He also met quite the character while in Nagrand: Garrosh Hellscream, son of Grom Hellscream. Garrosh had grown lethargic and depressed, under the impression that his father was shameful, as he had been the first to drink the Blood of Mannoroth. Thrall puts on a light show for Garrosh, to show him that his father died a hero. He plays out the scene of Mannoroth's end for the son of Grom, and Garrosh lets out a triumphant battle shout.
That brings us to the present.
It has been said a time or two that Garrosh Hellscream will be the new leader of the Warsong Clan in Azeroth, and will become very aggressive. It's possible that Thrall's attempts to cheer Garrosh up have had the wrong effect, or an effect more extreme than intended. It's very possible Garrosh may go down the same path Grom did with his ferocity and blind violence, but we can hope that isn't the case. If it is, we can also hope that Garrosh is snapped out of it before he needs to take his own life to redeem himself as his father did.
Overall, Thrall is the best possible leader for the Horde, though even he has his weak points. He is very trusting of his own people, and willing to put the wrong people in power because they're his friends. He is also perhaps a bit naive, attempting to foster the old ways of the Horde while pushing them forward at the same time. Regardless, there is no one that even comes close to his ability to lead the Horde, and may his reign be long and fruitful.