I just did today and it was a LOT better than i expected. For those who don't know, it's a set of 7 memories akin to the Desmond memories of the main game, but following the life of Subject 16 - Clay Kaczmarek. It's £8 which is kind of expensive for something that's only about 2 hours (if that) long, but it was definitely worth it since it adds a lot of new information, as well as actually developing Clay's character more (hated him before since he was some insane crazy nutjob but now i can empathise with him), and a HUGE twist. So i'd suggest at least watching a playthrough on youtube or something.
The gameplay definitely improved on the Desmond sequences (which i quite liked but i know lots of people didn't), there's a new 'block' as well as lasers as obstacles, and of course a lot of returning mechanics like the particle streams and the orange no-placing-blocks field. More importantly than that though, the music and art design are amazing and in some cases gave me an overwhelmed feeling....which not many games can do.
If you're not going to watch a playthrough or play the DLC for yourself, then here's the twist for you....it's pretty important:
Spoiler:Here it is!
Lucy was a Templar all along!
While 'infiltrating' Abstergo, Clay sees a security tape of Vidic and Lucy talking. Vidic is telling Lucy that if Desmond doesn't cooperate with the memories of Ezio Auditore, she should take him somewhere 'comfortable' (with the Assassins in the van / to Monteriggioni) and then Abstergo will retrieve the data later. Afterwards in the level you find an email from Lucy to Clay, where she tells him that she knows he knows, and that she has deleted the footage and will no longer get him out of Abstergo (like the Assassin order had assumed she would) because she can't have William knowing.
MINERVA MAKING DESMOND KILL LUCY AT THE END OF BROTHERHOOD MAKES SENSE NOW. HOLY SHIT.
Just watched it all, there's no way I'm buying it. I cba to do the Desmond ones anymore
But I suddenly have a lot of sympathy for Clay. He seemed to be pushed around by everyone in his short life, his father, the therapist (assuming he was the patient) his mother, then the Assassin's didn't care much for him to not get him out when they knew very well he was in there, and he went willingly into Abstergo.
It's very sad. He's a much more interesting character than Desmond.