By Slanted Light

I've only got season 3 - the rest is a pretty dim and distant memory (though it felt weird to see David Marciano turn up as a seriously slimy creep in The Shield!). This is the season where the original Ray Vecchio goes off undercover in Las Vegas and is replaced by Ray Kowalski who is in fact undercover as Ray Vecchio ..... *g* It really is very enjoyable - just so much fun, taking itself seriously in terms of quality but also having fun with lots of cinema and TV tropes. Hope you enjoy it as much as you expect!
I thought it was interesting that Paul Gross was apparently quite fanfic-friendly and slash-friendly in an abstract sort of way (and I was going to add something but I don't know if you want to avoid being spoiled!) If you should ever feel in the mood for a bit of fic, though, I can recommend some amazing authors. I was never really active in the fandom or anything, but I read around a bit ... *g*