Deadly archery is fine - so long as NPCs have the same level of deadliness towards you.
I'd hate to be able to stand their taking shots like a pin cushion, whilst waiting to get off my one deadly kill shot - a real immersion killer.
I like this idea. Not noticing a hidden enemy archer that's in a room... He should be able to spot you (possibly). If he does and he gets off a sneak shot on ya', you should have to pay for not being more cautious. That seems reasonable to me.
But then again, the stealth factor of the game in Oblivion was pretty untenable. It needs a major overhaul, and we need to see what that looks like when it's done before we can evaluate how well any other aspects of the stealth play are going to work.
I wrote this in another thread:
Stealth in general needed some work in the last game. One of the major handicaps to archery, among other skills, in Oblivion was that any action taken while in stealth mode would result in someone instantly seeing you, even if they had no idea what was going on.
As a Master Marksman one of the perks is that you can paralyze someone with a shot from a bow. I would also use paralyze poisons on the arrows. I recall shooting a target and every single time, despite that they had their back to me, I had been totally hidden, and they were now paralyzed, they would suddenly know exactly where I was.
More importantly perhaps, so would
every other creature within a 50' radius.
Something resembling the Dukes of Hazard would then take place, where I would take off like a bat out of Hell down the length of the cave or hall, giving as much ground as I could, taking corners quickly, and generally trying to shake my pursuit.
Even if I was several rooms away from the pursuers and had taken several turns - thus they had no direct line of sight on me at all, they'd still know where I was and continue to close in on me. Conjurers would get near me and although I was still hidden, they'd know exactly which room I was in. They'd then summon a monster and despite that I could normally hide from that monster easily, it would - upon spawning in the room with us, know exactly where I was an immediately attack.
This made the concept of "stealth" pretty preposterous.
If they simply improved the stealth system in the game and actually played through with it this time in testing, making it serviceable, it would not only be a significant fix to stealth play in general but would also have a major impact on swords (which get a 6X strike if someone is hidden) and archery (which gains a 3x strike if hidden).
An improvement in stealth would go a long way to improving at least two other skills as well.
Stealth in general in Oblivion needed a lot of work. Without correcting those fundamental issues with stealth, any other improvements become rather moot.