As far as DLCs go, "Dead Kel" is definitely one of the better ones I've seen, both in terms of providing bang for your buck, as well as improving upon Reckoning's gameplay template. One of the things that really bothered me after sinking several hours in the first game, for instance, was how the combat began to get monotonous, as there wasn't nearly enough variety in enemy encounters or types to sustain the game for the advertised 200 hours. In "Dead Kel", that has been improved substantially. Not only are there new and more enemies to find, but they have more interesting tactics as well - the Scavs, fast-moving predators with scythes for arms, are both fast and powerful in melee, but can also launch persistent area-of-effect attacks and even blow themselves up if you try to take them down too quickly. Root Golems, meanwhile, can tunnel underground and fling Boggarts (smaller enemies) at you. This goes hand-in-hand with a general reduction in trash mobs to fight, and more memorable encounters with varied enemy composition.
Another thing that's been improved is the overall pacing and quest design. Reckoning tended to go off the rails due to the sheer number of quests and locations available, and while much of that content was interesting, it was often drowned out in all the random fetch quests and dungeon crawls in between. The smaller focus of Gallows End means that "Dead Kel" can tell a more forward-moving story, and the side-quests it does offer tend to tie in with the environment and story arc a little better. Granted, it's not fine literature by any means, but combined with the greater variety in environments and enemies, I found myself much more compelled to keep moving forward and exploring.
There are still some improvements I think could have been made. Gravehal Keep, though great as a long-term goal, doesn't really do much to spice up gameplay - once upgraded, it more or less gives you daily loot drops, a standard suite of stores and services, pet-raising (which really just works out to "choose what stat boost you want"), and a few repeatable fetch quests. Considering the way Gravehal Keep is established in relation to the island's other inhabitants, I would have liked to see it factor into the main story more, perhaps even causing a schism between the Akara-worshipping dirt farmers and the more industrious members of society. Building it up in order to take the fight to Dead Kel himself, complete with a brigade of pirates of your own, would have also been a great gameplay twist. As it stands, the whole thing is sort of just a big XP and loot factory.
There's also dungeon design, quest design and loot balance. Some of the dungeons in "Dead Kel" do get pretty big, especially the final one, but most of them are still quite small and fairly linear. There are one or two which definitely do have branching pathways and even secret ways in for stealthy players, but they're fairly rare and I think more could have been done (though it's still a step up from many of the main game's dungeons). Quests are also lacking in choices compared to those on the mainland, and there are few opportunities to use non-combat skills to solve problems. Perhaps suffering from "DLC syndrome", Gallows End is positively bursting with new items, many of them very powerful, to the point where perhaps there are a bit too many of them. Unique and set items seem more common than regular ones from time to time, and despite only gaining a few levels during the experience, my character was significantly more powerful than when he first arrived simply because the equipment was so much better than what I was finding back in the Faelands.
Last, it might just be the old-school PC gamer in me, but I would have liked more of the additions to factor into the main game as well. "The Legend of Dead Kel" is very much a self-contained experience, and while Reckoning hardly had the most urgent story, the fact that none of the new enemy types or items seem to show up in the rest of the game world, or that there are no new quests added there, is a little disappointing. I'm a big fan of traditional expansion packs that add onto and enhance the existing game, rather than providing new campaigns entirely, so I would have appreciated a bit more of a tie-in with the main campaign.
Despite my list of quibbles, "The Legend of Dead Kel" is definitely one of the better DLCs I've played in some time. It's got a great theme and look, the story is engaging enough, and I think it executes better on Reckoning's core gameplay than the original game does. While it isn't quite as cerebral as, say, Fallout: New Vegas' add-ons, and I have trouble imagining anyone who needs even more content out of Reckoning, for those interested, Dead Kel's legend is definitely worth hearing.