The first incarnation of what could become a pair of legendary rogue daggers is pretty easy to obtain. The two parts of the quest line that are potentially the most difficult are: finding a dragon soul raid group that has killed the first 3 bosses and will let you pickpocket the fourth after the trash is cleared, and getting together and subsequently parting with the non-negotiable 10k gold required to complete the second quest.
The pickpocketing itself is very easy and rumors of a 15 minute wait between rogues is greatly exaggerated. A rogue can pull the boss, vanish, and proceed to pickpocket a freshly respawned quest item with no waiting (unless your vanish was on cooldown for some reason).
Many groups have been charging rogues admission to come in and pickpocket. Certainly a good option for anyone who isn't part of a sufficiently progressed dragon soul raid group, and also doesn't know anyone that is. It's really no trouble at all to bring in a rogue with a mass summon while the group takes a short break they would have likely taken anyway.
Oh, and most importantly, remember to turn in your pickpocket quest before you leave the instance and pick up the next quest. If you don't you'll have to find another raid instance to enter just to turn it in.
So now you're no longer at the mercy of a raid group, you've spent your 10k, it's time for the fun part. These quests are a lot of fun, almost worth the 10k just to play the rogue minigames. The first "warmup" quest is to infiltrate Ravenholdt Manor without being detected.
I won't spoil any of the fun, but there is a new stealth mechanic for these quests where you have to evade mobs with heightened senses. There will be a large red circle around your feet showing how close you can get before being detected. There isn't any wrong way to sneak around the mobs so long as you get past them, and if you screw up a few times you get ported back to the beginning to try again, no penalty.
You'll be using pretty much every ability in your rogue bag of tricks to complete these stealth quests: you can sap a mob so you can walk through it, you can distract mobs so you can walk behind them, vanish or cloak of shadows will both remove your red circle temporarily so that you can sneak around as if the mobs didn't have heightened senses, and if you are specced into subtlety you can shadowstep behind mobs and continue undetected.
The manor is easy to sneak into, I got it first try without any prior knowledge. The real fun is on the next quest where you need to sneak deep into Gilneas. It is pretty much a trial and error process of finding a path through that works best for you. There are a lot of pats walking all over the place and there are very narrow corridors through which to sneak between mobs. A lot of time is spent sitting in a safe spot and watching for where to make your next move.
You'll be happy to know that when you make it to Creed you don't have to sneak through all the mobs again if you fail to kill him. You get to run right back to your corpse and try again. Rumor has it that even if you leave the area to do something else you can fly back to Creed directly on your mount.
Both of my rogues specs are subtlety; I have a leveling/survivability spec and a raiding/damage spec. I of course did all these quests in my sneakier survivability spec with shorter utility cooldowns and more self healing. Since my damage was pretty low as a result I had to go the route of using blind (preferably glyphed to remove dots) to reset his enrage timer between damage bursts. Assassination and especially combat rogues will have an easier time of beating the two minute enrage timer, but they can only use blind once during the fight to reset the timer.
The fight is mostly move out of circles and avoid his frontal cone breath attack while beating the crap out of him and interrupting his one other spell which hurts a lot and drains energy. You'll also be using damage reduction cooldowns and stuns as often as possible to reduce your damage taken and get in some more powerful attacks from behind (unless you are combat and face roll him from the front).
If there is someone else attacking Creed when you get there, rumor has it you will get credit for the kill just for being there and get ported back to the NPC to complete the quest. So you have the choice of helping to kill Creed and perhaps annoy the rogue wanting to solo him, sit back and watch potentially never getting a chance to try Creed yourself, or fly away and come back later to do it yourself. I'd say if you get put in that position, you should just help kill him and get your daggers.