There's a game called Sniper Elite on steam (and I guess elsewhere as well) that sounds like what you're looking for. I haven't played it so I can't say anything about its quality, but if the trailer is anything to go by it should fit at least some of the points on your list.
Sniper Elite is indeed a great game worth your time. Though on some levels it might cause you a bit of frustration.
Realistic ballistics, aiming and all that jazz.
Sniper Elite has both bullet drop and wind in the options. There are also many techniques to steady your aim like manually breathing out.
Single Player focused (skills have gotten a big rusty)
Yes, though I think there's a multiplayer mode as well, not that I have much hopes of there being a community that's still playing it.
Decent graphics (optional but still good to have)
It's passable for what they need to accomplish.
Would love "scopeless" rifle sniping
You can try shooting without the scope
.
Sniper Duels (though this is more of a multiplayer thing)
There are certain parts where you are going to have to find and take out enemy snipers.
Bullet and/or killcam
Yes it has this.
Storyline (something different than an American gun wank for a change).
You are an American, but his nationality doesn't feature very heavily in the story.
Open ended levels (for different tactics and all that)
Oh yes this. There are some missions that aren't very open, but for many of the missions, there are a lot of approaches to competing the objective. You're usually placed in a wide open area with bits of cover and artillery craters littered around for hiding. There's one mission where you have to stop three vehicles from leaving the staging point and you're given a bit of time to plan how you're going to stop them, scout the paths that they may take, and set up traps if that's your fancy.
Stealth/decent AI (no Farcry enemies seeing you hidden in a shack 50,000 kilometres away)
On hard, timing your shots with landing artillery shells is going to be very important. There's lots of non-sniper shooting in the game as well if you so choose to pick up those weapons. All in all, you can't take much damage on the difficulties above medium, for the most part, you're going to have to take some shots, and run away from overwhelming forces if you bump into them unexpectedly, but they're usually not a problem because you're leading them into some traps you've set up, right?
Infromative HUD (displaying wind direction and the like)
I think so. It's been a while since I've played this.
Replay value
The missions have a lot of replay value in that there's quite a lot of ways to accomplish them. Though there are some levels like the one where you have to provide covering sniper fire for a fleeing PoW that don't offer much wiggle room, the area leading up to it certainly does.