I'm not sure exactly what I thought was going to be behind the mid 20th century vault door, but it certainly wasn't Wesley Crusher. I didn't hate it either. Was the sweater that he was wearing one that he wore in TNG? It seemed very familiar.
The Loom are terrifying. We've seen "getting erased completely from history" before with the Krenim time weapon (VOY: Year of Hell), but this version seemed so much worse to me.
I loved the bit regarding all the separate realities, including the "oops you aren't supposed to know that" regarding the mycelial plane.
Seeing Janeway take on the Loom by herself in a shuttle reminded me of her taking on the macrovirus in VOY: Macrocosm.