The general essential concept seems to be that leaders and defenders are melee, controllers are ranged, and strikers are mostly melee but with some ranged options.
A slayer still gets the Dex bonus with a bow (and has proficiency with it, not to mention at least ok Dex to use it), but most other class features don't help. Similarly a scout has good dex, and can actually make use of some of the stances (since they are for both versions of the ranger) but doesn't get it's primary striker mechanic. The thief rogue can use ranged attacks, but needs to stay close to be able to use backstab. The hexblade gets daily implement powers, but still wants to be adjacent for it's boons, not to mention it's at-will and encounter powers.
So, for the assassin, even with the ranged build, you are primarily attacking with a melee weapon (although, you have 4 at-wills in all).
The guild choice mostly comes down to one choice, really. The bola takedown and unarmed throw are practically the same (both do min damage and knock prone) as are the poisoned dagger and precision dart (both deliver poison on a miss, or cause a -4 to the save against the poison on a hit).
So, really, the choice is between Garotte Strangle and Quick Shot, the latter being pretty useful (it let's you shift afterwards and can be used in closed quarters, although how often it will be better than just using a melee one hander is questionable. [I guess you still get the shift afterwards, or you could shoot someone other than the person adjacent to you].
As for Garotte Strangle ... it's very odd that they put Charisma as a secondary stat. True, some of the skills would be useful for an assassin, but outside of level 8's flawless disguise, and a few utility powers, there is little use for charisma for the Assassin. If anything, a solid constitution is probably the best bet, giving some extra hardiness and improving fortitude defense for grabbing.
It's a little dissappointing compared to the playtest, but it still has the daily poisons and the "one super encounter power", so it isn't all bad.