They still didn't get it right. Marginally better boss fight, worse everything else.
This DLC is basically a short game made with the same engine as the latest Deus Ex installment - Human Revolution. As such, the gameplay is exactly the same, so I will skip over that.
It's a game within itself (quite literally - it runs out of its own folder, with its own set of files), but what this DLC set out to do was "Fix" the boss fight at the end of the main game. For those not in the know, the boss fights were handled by another company, and many of the fans, and Square Enix, were not happy with the result. Essentially, they wanted to show their fans how they would have liked the boss fights to be, but if this was the result of that thinking, I think they misunderstood the problem.
The complaint to the main game's boss fights were that they consisted of just you in a small room (which has the feel of being artificially set up for that purpose) with your opponent, and you have to kill them with your guns. This is not actually contrary to the Deus Ex series - it is full of instances where you have to kill certain people in order to progress. The difference was it was handled (generally) in a more tactical fashion. Even if the battle amounts to "Get out your biggest gun and shoot!", there would be skill in the preparation for it eg. hacking turrets, laying traps, studying your environment etc..
Deus Ex: Human Revolutions is missing that element in their boss encounters, which is a pity for an otherwise good game. In The Missing Link, it feels like they have addressed the lack of choice in how you deal with the encounter, but at the end of the day (without giving anything away) it is just a room, with one entrance, with enemies in, and your choice is either to kill or sneak.
At the end of the game, I wondered "did any of this matter?" In mid game there is a choice to be made, but it turns out to have no impact on the ending save for some dialogue. How is this an improvement?
Of course, what everyone will say about "The Missing link" is that it is too short. Of course it is short - as a DLC it should be thought of as a minigame. However, I felt that was no excuse to re-use the same mission area to death, or leave out an important part of the deus ex series - character interaction! The loose end that the game fills in, is wasted for it missing this essential element.
This DLC had the potential to be an excellent short story accompanying the game. Such a shame it isn't. As a game within itself I would give it a 5 or a 6, but as it is sold as a DLC, I went up to 6.5. It suffers most from lack of story and repetitive environments.
Even if taken in context as a DLC, it is not anywhere near as good as "Human Revolutions", despite that game's flaws.