Question: I'm 1/4 through my first novel, with a pretty solid 12 page outline of the whole thing. After years of reading books about story structure, I think I have a good grasp on how to make a plot work.

My characters, however, are turning out to be quite flat, uninteresting and generic. They do have motivations and I'm putting a lot of effort into making sure they act accordingly, in a logical way according to their goals and the story seen from their perspective, etc. But they don't feel "alive".

I've read about the archetypes in The Writer's Journey, but that's about it. How can I make my characters come to life?

Answer: 
Finish the book, then go back and look at the characters again.

When I start writing my characters are fairly generic, flat, and frankly cardboard. Character is my weakness, I love plots and ideas.
The crucial thing is that in the second draft, I then go back and add in bits of the colour, life and uniqueness which the characters have only accumulated by the last chapter.
Sometimes this will require changes to the plot (I'll realise that Rachel shouldn't have done that in Chapter 2, it doesn't fit with a part of her character I only realised in Chapter 7), but overall I find this a much more organic and natural process than trying to specify everything about a character before I know them, and as such the results tend to be much more convincing and compelling.

Your mileage may vary, but I think if you're a quarter of the way through without your characters having sparked yet, you're probably more similar to me in this respect than most!
I think one of the problems with character development in novels is the author's liberty to spend periods of time explaining a character's motivation to a reader without the character actually having to say or do anything. A chapter that has the ostensible position in time and space of someone sitting in a chair, reflecting on a dramatic problem, is something that crops up from time to time. That reflective period can info dump a whole heap of incidents in summary and leave the character in a position where the next things they say and do are obvious to everyone.

The problem with that is that doing this is dry and it restricts the things that you need to have the character do in order to establish character through action. It also means that you miss opportunities to flesh out character through interaction and action.

There is nothing wrong with having a character make a seemingly bizarre action that they later have to explain, possibly to another character. Also it is possible that characters don't always agree with each other's motivations. These nuances of character are what flesh out the interactions and make each character grow and deepen.

I lucked into character development boot camp, I did a film-making course where I wrote a lot of scripts. They weren't great scripts but they taught me the nuts and bolts of what do when you can't just gear-shift into "exposition mode" and have a slow beat of characters reflecting on their own pasts.

If a story can get by with out that kind of thing it will be richer for it. It is a path that should only be taken when absolutely necessary. Always explain exactly as little to the reader as you need to in the moment to keep them reading the next few paragraphs. Info dumping is the gentle story killer, smothering under the guise of explaining.