I'm re-reading Julian May's 'Saga of the Pliocene Exiles' for the first time in a decade or two. I love the fecundity of the world-building, the audacity and inventiveness of the premise, the vast submerged mass of information about the Galactic Milieu that is out there hidden from our sight; I like the outre characters. As a long-time RPGer, I like the gamified classification of psionic powers. I don't mind the lack of character development many reviewers complain about. After all, the main characters are either denizens of the Land of Faerie - whose characters cannot develop as a literary convention - or profoundly messed-up people subjected either to compulsory happification or brutalisation that is only likely to mess them up further. Even the way the two most unlikeable male characters are unconvincingly transformed by 'True Love' is reasonable if you assume they are wartime romances that are not going to last: the female Exile population would be rich in the sort of sad cases who fall for men like that, and that kind of desperate clutching at affection is common under that sort of stress.
But as a story... coming back to it... it is not my kind of story. It is not the way I would have done it. All the glorious world-building is frittered away. For me, at any rate.
My many years of GMing have conditioned me to prefer the 'slow unfolding of a mystery' to 'whirlwind of action' and I would have written this story as more of the former.
Even though the society of the Galactic Milieu is less pathologically risk-averse than our lame-arse one, it still seems unlikely that they would let Madame Guderian send people willy-nilly back through time for sixty years without regulating her in any way, and stranger that they would just take over her enterprise and keep it running without doing any investigations of their own. It doesn't make sense that Madame Guderian would just have kept going, after the third or fourth time she sent a time-traveller off with amber tablets and instructions on how to attempt to get a message back to her, and heard zip. Or, that she wouldn't have communicated her suspicions to someone else. So, in a more realistic, plot rather than action-driven scenario, the third or fourth time she would have gotten a message back saying things were initially bad in this area, but now it is secure, and we're all fine here thanks, how are you? And over time a whole plausible story could have been built up mirroring the 22nd century expectations about what the Pliocene is like, feeding information to improve the chances of future Exiles and coincidentally milking the future for particular items and materials wanted in the past. On the basis of this plausible story, it makes sense that the Milieu would keep the business rolling after Madame Guderian steps through the portal herself. The first novel will end as the characters step through and discover this story is a complete fabrication.
Actually, no, thinking about it that will drag the pre-story out too long. Instead, Group Green will arrive in the Pliocene halfway through the first novel, and find that superficially it appears much as reported - the Tanu will stay well in the background at Castle Gateway and it will all be carefully managed to stop information from leaking back into the future. Only as they travel on to the next stage, in the second half of the volume, will the fabrication emerge.
As written, the procedure for handling the time-travellers at the Pliocene end is incredibly messed-up. There would be a procedure for stripping incomers of blood-metal artefacts: it is not hard to drag them off for a delousing and have some human who can recognise iron go through their loot. And so much of the future plot hinges on the ridiculous accident of Felice's latent superpowers not being picked up: it is silly, and it wouldn't have happened. In my version they will be smoothly processed and carted off in appropriate directions without unseemly violence, and Felice will have to escape later.
Now, in this second half of the first bit, while the fabrication is revealed, the full malignity of Tanu intentions will be hidden from the characters, and from us. That can wait until book two. The enemy in book one can be the Firvulag: they don't control Castle Gateway, but are obviously keen to deny the Tanu the use of the humans, and make use of the more valuable ones: they can attack the northern party and capture them, and it can be they, rather than the Tanu, who subject their captives to a brutal sorting process. I know this makes the human characters more dried leaves tossed by the winds of fate than the Omnipotent Captains of Their Destinies, but damn it, at this stage they should be victims of fate, and that whole John-Campbellesque 'aren't we humans just so damn precious and special?' shtick is soooo 20th century.
I would like a whole second novel of Group Green's largely peaceful integration/failure to integrate into the world all that world-building went into: let us care about them, and the people who are already there, as people rather than hyperkinetic action figures. Through the course of this book, it will become apparent that the Tanu, as well as being liars, are considerably blacker than we thought at the end of book one; and the Firvulag considerably greyer. Layered over this, I would introduce a second group of 'special' time travellers, Group Aquamarine, say, whose back story will move more quickly than Group Green's. This group will contain as one of its members a retired member of the Portal Administration who has been reviewing all the correspondence going back through Madame Guderian's time - it has not been that long that the Milieu has been operating the Portal, after all - and has isolated all sorts of puzzling inconsistencies in the data. So he/she/it (why have no mentally-unbalanced Simbiari taken the plunge into the Pliocene, anyhow?) has volunteered for a one-way fact-finding mission to ascertain the facts on the ground and send a report back.
And then, well, in books three and four we can let loose with all the action scenes and wholesale slaughter.
That's how I would have done it.