If I like the DCI Ryan books by LJ. Ross...

[SDTGisAnEvilWolefGenius]

...what other detective fiction will I like?

I also enjoy Ann Cleeves, JD Robb, Dorothy L Sayers, Ellis Peters and Kathy Reichs.

If you like Dorothy Sayers, you might enjoy Margery Allingham and Ngaio Marsh, from the same era. They are both lovely, subtle writers. Georgette Heyer wrote a series of detective novels which are an absolute hoot ( apart from
Penhallow which is a dark character study).

If you like Ellis Peters, have you read her George Felse series? I prefer them to the Brother Cadfael books.

Reginald Hill’s Dalziel and Pascoe novels are beautifully written and frequently very funny police procedurals. I also like Alison Taylor’s books set on the Welsh Border.

You could try Rebecca Tope’s Cotswold mysteries, which are gentle and engaging.

I really enjoy DM Greenwood’s ecclesiastical mysteries featuring Theodora Braithwaite.

If you enjoy Kathy Reichs, have you tried Tess Gerritsen’s Rizzoli and Isles series? I prefer them to Kathy Reichs myself.

I have read some of the Tess Gerritson - I'd forgotten about that.

There are some great ideas there - many thanks!!

You might also like JD Robb's Eve Dallas series (US based) - first is Naked in Death. (and if you like that, you may also like the "Richard Castle" Nikki Heat books, though the first three are better than the later ones, or SR Garrae)
I can't remember who wrote it but someone followed on the Dorothy Sayers books, and wrote some others featuring Imogen Quy.
Also Minette Walters (quite dark).
Janet Evanovich is very light and slapstick, but fun and easy.

I love the JD Robb books - but I hadn’t heard of Nikki Heat, so I’ll have a look at her books - thank you.

Richard Castle is the author (it's a spin off from the TV series) - Nikki Heat is the main detective. If you liked the series Castle, these are the books the character "wrote".