The finalized, non-accidental executioner class is available for download. Having read over the class for like the third time I think, my original opinion still stands: I like it a lot more than the shadow-only assassin. This is based on the fact that when I compare them side by side, the executioner just feels like more of an assassin. This is partially due to the fact that the assassin has plenty of specialized attacks that let them roll out an assload of damage--assassin's strike and attack finesse for starters--but also because the executioner regularly utilizes poisons, something I have yet to see any of my players do in any edition of D&D.
Having seen the assassin in play up to 6th-level in a Scales of War campaign, I can say that it's mechanically sound, but conceptually I have a hard time working something together in a satisfactory manner. Shrouds aren't well explained, and the class seems to focus on utilizing shadows to tear, stab, and poison your opponents. Also, the idea of trading part of your soul for "shadow-power" seems better suited for something like a necromancer or warlock, while the assassin as written makes me think more of Pride.
Really, I don't want to reiterate most of what I'd said in the past (which is what I'd be doing if I tried to go into detail again). Most of the class features and powers were very similar to the playtest versions, with some formatting and balance tweaks here and there. I found the accompanying Design & Development article to be an interesting read, as you get to see why R&D did what they did with the dual-power sources, assassin's strike, poisons, situational at-will attacks, etc. Whether you're pleased or pissed at the direction they went, it might inform you about their reasons for doing so.
It just sucks that they didn't update Character Builder with the executioner, yet. >_>