At its heart, the Great Hall is an exciting and well-tuned skirmish, and providing that you take Thunderspire's regular gaffs with a grain of salt players will probably have a great time here.
This is the Horned Hold's "southern fortress". It lies directly south of Urwol and the portcullis, with a narrow tunnel connecting the two outposts. (Note that north is to the right on the encounter maps.)
The essence of the encounter is a "levelled up" version of the fight the players have just won against Urwol. The orcs from the last area are replaced here by Duergar Guards, who pack a mean warhammer punch, and they're backed up by more of Urwol's Duergar Scouts.
I didn't mention the Scouts in the last post; they're more understandable if you think of them as Duergar Rogues. They can turn invisible roughly every second turn and they do bonus damage when they have combat advantage. In the cramped terrain of Urwol's smithy they were pretty useless but in the more tactically complex Great Hall encounter they can really be a threat to players.
Urwol's role is filled by Rundarr, who's bigger, meaner and all-round more interesting than the Master Smith. Rundarr is an Elite, he comes with 180 hit points, and like the Duergar Champion's he's based on he has the ability to grow in size when bloodied, assuming a Large size template and rolling an extra +2 to hit and +5 on damage. Ironically, this much more memorable opponent only gets a single line of characterisation - "Rundarr's temper is legendary among the Grimmerzhul, who are bad-tempered by nature" - compared with Urwol's three redundant paragraphs of roleplaying notes.
I've written previously that Thunderspire Labyrinth is training players to control "adds", the additional monsters that might join an encounter if enemies are allowed to flee and find allies. Starting now, they're going to have to demonstrate that they've learned the skill.
If any of the enemies from the Duergar Workshop escaped, they'll flee here and warn Rundarr's troops, giving the otherwise scattered Duergar a chance to take up optimum positions. Later, when Rundarr falls, the rest of his command will flee to alert and join up with the western fortress, who as we'll shortly see barely need the help. If players want to keep fighting balanced, winnable encounters they're going to have to take steps to stop the beaten Duergar from escaping.
Almost as an afterthought, this area also contains three human slaves. They're named Arum, Bessa and Calder (only marginally better than Slaves A, B and C), and while they're not the captives the players are looking for they do know the western fortress and make daily trips there to bring the captives food. The module doesn't take the step of saying it, but one assumes clever players could use these characters as part of a plan to gain a slightly less suicidal access into the the western fortress and the "main" area of the Horned Hold.
Probably the biggest issue with the Great Hall is that it's redundant. Players can skip it and move straight to the western fortress (as mine did) and there's nothing here that advances the plot, enriches the atmosphere, or rewards players for exploring. The Horned Hold isn't such a fun area that you'll want to prolong it, so while it's not a bad encounter in its own right it's ultimately just getting in the way of a focused, excitingly-paced progression through the Hold.
 Cut the Great Hall out entirely and use its monsters to replace the ones in the Duergar Workshop. Rename Rundarr as Urwol but still use Rundarr's stat block in preference to Urwol's. You'll have one tight, tough encounter rather than two loose ones, and Urwol will now survive long enough to do some talking and give the Horned Hold some of the personality it's otherwise lacking.