Suggestions
Deadly Shadow: Gain +6 Dexterity and +6 Intelligence and 7.5 Melee Power.
Reason: Sneak attack dice greatly favors one specific weapon style. Also, if I'm going to capstone, I better be able to get an Assassinate DC at least within range of a multiclassed Coup de Grace.
Execute: You make an attack with +13 double strike, +13[W] damage, and +13 critical multiplier.
Reason: I really don't like the 1000 flat damage. Rather than give out consistent damage, I'd much rather have 200 damage misses 70% of the time and 3000 damage crits 30% of the time. There's a psychological reason for this. I'll remember that huge number and put it in my bio. But a constant 1000? Nope. Same DPS but much more "fun". It also scales better for when DDO goes Epic level 30.
Measure the Foe: Gain +5 Melee Power, +2 Dodge, +2 Maximum Dodge, +1 to hit and +1 to the DCs of your Assassinate ability for every 4/2/1 seconds you remain stealthed. This effect stacks up to 5 times and lasts for 10 seconds after you come out of stealth.
Reason: If I have to invest in hide skill, move silently skill, and crawl around slowly in the dark, that damage bonus needs to be noticeable. Especially if this ability has very little use in a raid tank-and-spank.