While they're not first person shooters (they're third person action/stealth games), the Hitman games -- particularly
Contracts and
Blood Money -- have nice assortments of weapons that are often very detailed. The way the player character (47) handles and reloads his guns is also very good for games of this type.
A video I made of the target range in Contracts
If you're looking for a more-realistic-than-most multiplayer FPS, I highly recommend
Insurgency. It's actually a mod for the Source engine (and free!), so you just need any game built on that engine (such as
Half-Life 2) to be able to play the mod. It's a multiplayer-only tactical shooter based on the conflicts in Iraq/Afghanistan. It's pretty high on the realism scale. I'd say it's somewhere in between Counter-Strike and the pre-Vegas Rainbow Six games. Whatever the case, the weapons look and sound great, are animated beautifully, and they behave pretty much exactly how they should. Pistols, shotguns, assault rifles, sniper rifles, light machine guns, the RPG-7... there's even an FN FAL!