Stylistically at least. I always thought the Morse books well-written, and Ruth Rendell's. P.D.James occasionally does wonderful descriptions of characters.
As a rule, in style (vocabulary and sent. str.), crime novels run the gamut from the erudite to the level of YA or below.
The Friends of Eddie Coyle seems to me to be stylistically really strong.
It's not just the brilliant dialogue, but the way the authorial voice is usually absent, allowing the narrative to unfold so that the reader is alone in working out what's really going on.
It's rare to read a story without the author or hero offering a guiding point of view, and quite a challenge to write, it seems to me. Terrific novel.
I just finished rereading Eddie Coyle. Great book, one of the granddaddy's of the hardcore crime books. The new edition has a great intro from Denis Lehane. I highly recommend it.
But I think the reference here is that new group of mysteries that read and feel like a literary main novel.
James Ellroy pushes the boundaries. The Cold Six Thousand is probably the most 'out there.' I just finished reading Blood's a Rover and it doesn't push the stylistic bondaries quite as much.
If it's like music then The Cold Six Thousand would be bebop jazz. Maybe earlier Ellroy and Ken Bruen would be more traditional jazz.
When the first couple of Patterson novels came out I was impressed with his idea to switch first person and third person narratives.