Wow, I thought I was gonna be pissed off from this DLC, after reading spoilers, but I'm not.
In fact, things are getting clearer and clearer to me.
-I partially expect Vega to be a sleeper agent who will be activated in a DLC (or not, without the DLC). He's still a good guy, but we know what very low levels of indoctrination do.
-There is a LOT of Control aspects and its leading to ruination in this DLC, which I expect Omega (aka *cough* Cerberus DLC) will also tackle.
-I don't mind that the Leviathans screwed up, and I do mostly believe their backstory. It actually still works with IT with me because...
-Hmm, nothing is still answered about HOW the 'Catalyst' (lol I'm sure Shepard is the true Catalyst) actually knows to take the form of a very specific Earth child that Shepard only met once and only mentioned like 2-3 times max in the entire game.
My biggest disappointment isn't that IT is disproven (its not), but that it seems Harbinger still gets a back seat after all his gloating in ME2.
Oh, and other note. If Leviathan can take the forms of people Shepard and it have known of, while capturing Shepard's mind, I wonder what the Catalyst can do

. I don't actually think the Anderson and TIM in the ending are real, and in fact we're experiencing a mixture of thralldom/direct control/indoctrination.
Oh and the oily shadows stuff still stands. The Reapers work off of the Leviathan methods. If some how Shepard is experiencing a special form of indoctrination overlay of reality (hello implants), then the oily shadows (as well as the VERY FAMILIAR music in both the Citadel scene and the Leviathan first level scene) is just one part of what is happening to Shepard.
Overall, I'm actually very interested in where the next DLC will take us. Bioware wasn't kidding when they said they would be aiming for LotSB quality for DLC, and I'm rather firmly convinced now that their financial plan for the game, to be sure of selling DLC, they'll be placing in the puzzle pieces in the DLC itself. (for better or for worse lol)
Oh and I expect a Reaper centric DLC at some point too. Leviathan deals with the origins of what created the Reapers, but I expect a fully featured DLC on what they exactly planned to do in London and to Shepard and more.