I enjoyed it. The squad banter was very nice to have as it's absence in ME2 DLC was always a pet peeve of mine. You can definitely see that they've been using the multiplayer as a testing ground for new game-play mechanics. The escort & power cell relay bits helped shake up what would otherwise have been some fairly dull combat.
The Leviathan themselves are fairly interesting and I like how it ties together several background stories like the 'Leviathan of Dis', Kasumi's lover's greybox, the rachni acting against their will and the origin of the reaper form. It raises a few questions though; if the Leviathan need "lesser" races to create technology and facilitate space travel for them, that means they had to have evolved on a planet with just such a race. If so, what happened to that first race? Did they become the Keepers? That would seem to be appropriate. I also have the wonder if there's a connection between Leviathan and the Thorian. Their MOs are very similar, so perhaps they evolved on the same planet? I mean Leviathan couldn't been the only branch of it's evolutionary tree, could it? I mean something that massive must have requited either a prey species of significant mass and/or enormous numbers. Perhaps the Thorian and it's thralls were that prey species? The implication there of course would be that Feros is the Leviathans' homeworld, presumably with it's oceans long since dried up. That or Thorian spores were somehow transported there at some point in the past...perhaps as a handy food source?
Overall, I can't shake the slightly hollow feeling that none of this matters, given we already know how things end...though it may make me rethink choosing the destroy option in future. I mean, with all the synthetics gone, what's to stop the Leviathan from enslaving all the lesser races all over again?
Oh and as for the severed Cerberus trooper head: I named mine Murray! And if you don't get the reference, go play Monkey Island 3.