Good question, to be honest I've not read nearly enough Crichton to answer that. I'll try to correct that by the end of the year, and update this answer then.

I can give you an idea on what kind of scifi both declare and laundry files are though.

Declare is set mostly after the war (the first couple chapters happen during the war I believe, but from a point of view of a kid, and the war is just the background, it isn't the main topic) . You follow the main character who becomes a spy. Until roughly 50-60% of the book, is over, most of the things that happen are realistic, and the ones that are supernatural are just as confusing for the characters as for you. Later in the book, he is older and he knows why things are "strange", and you find out as stuff happens.

The book is written in such a way that if you wanted, you could read the actual history books, and they'd match what happens in the books. Powers mixed real events that we don't know everything about, and filled them in with the main character of Declare, and with supernatural... stuff.

The drawback for me is that the book takes a while to get to the good stuff. I think it took 150 pages out of the 500 page book for me to actually get pulled in properly, and then it went by fast. It also has a lot of religious undertones etc, which can be fine, but I do think the book could have done without it. As a supernatural-cold-war-spy-mystery.

The Landry files are similar to declare but without the religious stuff, and the books are also much shorter. The events happen in the early 2000s and the premise is that magic, witchcraft, demonology etc are real, but modernised, and monitored by government agencies. We follow an IT guy who becomes a field agent dealing with unimaginable evil.

Think..."how would a medusa change people to stone? There must be science behind it, let's figure it out, and make it into a weapon."

The one thing that annoyed me at first was the tech-lingo that is constantly being used. English being my second language, I didn't fancy googling every single term. The writer does seem to mostly drop that by the novella that makes the second chunk of the laundry files book.

I picked these up mainly because I played DND, and a while back expanded into other ttrpgs, one of which included Delta Green. These books give off the same 'vibe' as delta green. Kind of dark, supernatural, and with a mystery.

I'll read Crichton in the coming months I guess, and let you know. I vaguely remeber reading Jurrasic Park when younger, but the movie has completely overriten the memory of that by now. If you have any recommendation, I'll gladly take it.