Mmm. It has been some time since I read Three-Body Problem and I bounced off The Dark Forest. This also means it's possible my impressions are either erroneous because I forgot something important or it's explained/ ret-conned in the subsequent books.

In Three-Body Problem as I recall there's some pretty hand-waving stuff about sophons in particular. They're basically a MacGuffin which is used to explain whatever is necessary to the plot so as to have the Trisolarans able to interfere in Earth's affairs essentially at whim yet not obviate the invasion itself. So that's not very Hard SF.

My issue with TBP is not so much the hand-waving, it's the attempts to explain things that quickly become ridiculous, because the author is clearly out of their domain of expertise. Sophons are one example - they would be more believable unexplained, but when they're explained as a circuit on the surface of an unrolled elementary particle, well...

Or sometimes it's the way something is set up in a particular way, only to be abandoned when it becomes inconvenient. For example, when they come up with a plan to set up a trap using monomolecular filament, it is specifically stated that it can only be made in that shape. But literally one page later, when the question of how to tie it to something without cutting through that something comes up, it's immediately dismissed by the same character saying that they can also make sheets of that material, so it can be used as a backstop. Either take is believable per se, but they're clearly mutually exclusive.

On the whole, the science in Three-Body Problem kinda felt like gratuitous insertion of random (and ften misunderstood) pieces of popular science into the story as a deus ex machina.