If you look away from 360, there's more options than you might think.
On PC:
SWAT 4, most definitely. Aside from the fact that you have to follow a bit more police procedure (and have cases following more mainline scenarios such as hostages and hostile suspect retrieval), it might as well be a R6 clone. Which is a good thing, in my book.
Battlefield 2 is also a fairly realistic game, almost to its detriment. There's a constant fight in the community over people who think they're getting shafted in game balance. Really they're just trying to play it like Counterstrike and finding it doesn't work whatsoever.
I have to laugh at anyone saying that Call of Duty is realistic, or compares to R6 in any way, though.