If anyone is looking for a great novel that partially takes place in Bletchley Park, I can highly recommend Cryptonomicon by Neil Stephenson (of Snow Crash fame).
Usual caveats about Neal Stephenson apply but I think Cryptonomicon presents a much more compelling portrait of Alan Turing than the film The Imitation game which incorrectly portrays him as a repressed nerd single handedly solving all the problems.
I don't know if this was what your parent meant, but
One of the fairly noticeable problems with Stephenson is that he uses the "rape as character development" trope a lot for female characters. So, that's not great. In general in fact female characters in his novels are not written as if they were - you know - people, and even when they're the protagonist we get some weird male gaze stuff going on.
It's not a deal breaker, Diamond Age is one of my favourite novels despite this. But certainly it feels at best lazy.
Other routine complaints are that Stephenson's novels are too long (fair) under edited (presumably with the same root cause, ie celebrity) and poorly paced (e.g. six chapters about the protagonist preparing and then eating cereals, two pages on the climactic bank heist they've spent the whole book planning)
Technically I think Stephenson suffers from having noticed that, unlike many contemporaries who wrote fiction set in the near future, he actually has some idea what he was writing about and not realising how limited that knowledge is. William Gibson knows he has no idea how a computer works, so in a Gibson novel he's not trying to convince you his protagonist knows which IPv6 routing protocol to use - William Gibson doesn't know what IPv6 is. But Neal might spend a paragraph about some nonsense that seems plausible if you know as much as he does... but then is laughable if you know more. That seems if anything worse than what Gibson chose.
I like hard SF, but hard SF is really difficult. One of my other favourite novels is Greg Egan's "Incandescence". Egan isn't great at writing women either, but in Incandescence he cuts himself a break, nobody involved is technically human anyway, but he did spend a lot of time figuring out all the tricky physics needed to make the novel's story work. Is there really a civilisation in the core of our galaxy? We'll probably never know, but Egan attempted to design a scenario that could, in principle, technically work.
