If I had to pick just one or two DLCs other than the ending patch thing, I think I'd probably go with Leviathan and From Ashes.
Leviathan because it addresses the root "where did all this shit start" question.
From Ashes because.. lol, Javik's lines are absolutely hilarious.
Also, did they patch in the third option at the end for Synergy (combining synthetics and organics) or did I misread your post? I thought you could do that as long as you had a high enough of assets accumulated by the end?