The Assassin is one of the new classes in Lord of Destruction.  She can be played a few different ways, and like most classes her skill choices need to be geared towards the method of attack she chooses.  There are a number of things Blizzard did really well with her, and some things that they, uh, didn't do very well.  I'll detail both in this report.

The Good

Speed kills.  In Diablo 1, I always stuck with my Speed/Haste swords on my warriors.  Kill faster and you take less damage, and swinging faster = killing faster.  Well, an Assassin takes this to the next level.  She can be PURE SPEED if you so desire with the skill Burst of Speed.  I've pumped this skill on my Assassins every time.  It provides a diminishing returns boost to walk/run and attack speed.  Play an Assassin with Fastest Run boots and level 7 Burst of Speed for a few hours and every other class in the game, including the Increased Speed Barbarian, will seem slow and sluggish.  She's that fast.  I haven't had the opportunity to try out an equipment setup focused on increased attack speed, so I can only imagine.  Her attacks are very fast using claws and Burst of Speed already, and having experience with a Zeal-based Fanaticism Paladin, I'd bet she attacks faster than the eyes can see.  If she were decked out with increased speed equipment, level 10 Burst of Speed, and a supporting Paladin with Fanaticism, could she reach 2 frames per attack (thus, 12 attacks per SECOND)?  Maybe.  I haven't crunched the numbers since I don't know the relative speed numbers of her weapons and what increased attack speed equipment exists in Lord of Destruction.

Her Shadow Disciplines are what sets her apart from other classes.  Burst of Speed's in there, along with Claw Mastery.  I consider those must-haves, while everything else is optional (thankfully, those are level 6 and level 1 skills respectively, too).  One of the issues you have to consider is in the left side of the tree, where Burst of Speed leads to Fade which leads to Venom.  Only one of these three skills can be on at any one time.  Guess what that does to Venom, a level 30 skill which adds (a lot of) poison damage to your attack - yes, it makes it rather useless, unless there's something special about the skill I don't know.  Fade remains useful since it adds resistance to your character, useful when in a situation that requires resistance more than a speed boost.  Even still, I tend to use Burst of Speed like an aura, constantly recasting it as it runs out, trusting in my ability to outrun any magical attack with my insane running speed.

Weapon Block is along the middle column of the tree, a skill that allows you to block while dual-wielding claws.  The best thing about it is that its blocking percentage doesn't get reduced by your character level and dexterity, like normal blocking with shields does.  Taking it to level 10 or so will give you a passive 50% chance to block attacks.  The worst thing about it is something that I'll get to in "the bad" section of this report.

Down the middle column is Shadow Warrior and Shadow Master, two skills I personally enjoy a lot.  Shadow Warrior is a skill many count out right away, put one skill point into, and wait for Shadow Master.  While I agree that one skill point should be enough, I don't know yet if we might all be too quick to dismiss the Warrior.  Shadow Warrior creates a duplicate of yourself who fights for you, like a Valkyrie.  She's much more advanced than a Valkyrie, however, because she mimics your skill choices.  Whatever you have on your left and right spellboxes is what she'll use as she's fighting.  You could use this to your advantage by hotkeying a trap skill and watching her place free traps for you.  Still, Shadow Master is probably what you'll be using once you reach level 30 - a duplicate of you with (usually) more hit points.  Shadow Masters can cast any skill an Assassin has access to, and I love it - sometimes I swear there's some intelligent AI in her choice of skills to use.  Stand still for a bit and she'll plant traps around you for protection.  Run into a big crowd and she'll cast skills to handle it, from Cloak of Shadows (blinds enemies) to Mind Blast (stuns enemies).  Sometimes she'll go in and get dirty with melee fighting; other times she'll hang back and cast spells to deal with the mobs.  I find that using her along with a cold mage mercenary makes for a wicked 3 person team while I am pure melee.

Most of my experience so far is with the Shadow Discipline tree.  Traps are generally used for crowd control - in fact, if you're a ladder player, you'll want to know that most of them use the trap tree a lot.  It's the only tree that contains skills to let you hurt many monsters at once significantly, and if you're going for quick level ups over all, that's your choice.  When playing solo, you can lay down whole minefields, drum up a huge crowd, and lead them to their doom.  I recall grinning while playing alongside an Assassin who laid a mean trap for Diablo by literally creating a minefield around his pentagram before we activated the final seal and let him out.  What a greeting.

The Bad

Sigh, the Assassin isn't perfect.  The main problem is that one of her main archetypes, the dual wielder, just doesn't work.  She suffers from the same bugs that the dual wielding Barbarian does.  Certain skills will only use one of the weapons every time, and the skills designed to use both weapons simultaneously (Dual Swing for the Barbarian and Dragon Claw for the Assassin) don't work as advertised!

It's clear from the design of the skills that Blizzard intended to allow Assassins to dual wield claws as a viable alternative.  Weapon Block ONLY works when wearing two claws, and Dragon Claw is a skill that lets you "attack with both claws simultaneously."  Simple testing shows this to be far from the case.  Just put a normal claw on one hand and a mana or life steal claw on the other and swing away with a bunch of different skills.  The only one that successfully uses both claws every time is, of course, NORMAL attack.  When using chargeups, you can tell just from the animation that only one of her two claws is used every time.  Verifying it by watching for life/mana steal "swirls" as you attack enemies makes this perfectly clear.

So, when using chargeup skills, you're only using one of your two claws.  And the claw that is used changes depending on the chargeup!  Now, couple this with what's wrong with Dragon Claw - it's supposed to use both weapons for one attack, but just like Dual Swing for the Barbarian, it doesn't work.  Put a mana steal weapon on the right side (left hand) weapon, and swing away with this skill.  You'll see the mana steal "swirl" only occasionally, and the damage boost just doesn't seem to be there.  I experimented with this, moving my mana steal claw from hand to hand, and found my mana slowly draining when using one configuration compared to the other.  The mana steal wasn't happening often enough when it wasn't the "primary" claw.

To make it worse, Dragon Claw has a set attack speed.  If you're using two Greatly Increased Attack Speed claws, the normal attack will be MUCH faster than Dragon Claw, which will use the standard attack speed every time.  So my dual wielding Assassin uses normal attack every time.  Pretty sad...thankfully, chargeups work with normal attacks as a "finishing move," but then the chargeups only use one of my claws at a time anyway.  I found myself ignoring that tree almost entirely.

At least I can use Weapon Block to get good blocking, right?  Well, yes, but when using your claws to block attacks, the durability gets reduced on them like shields do when blocking.  So not only do I have to repair my claws due to my attacks, but I need to repair them for my blocking too.  This sends me to town a lot, and good claws are NOT cheap to repair.  Still, that's just money, so it's not that irritating - however, if the issues with dual wielding aren't corrected in the final version, I will heavily recommend to all players to take the single-claw and shield route.  Assassins need high dexterity to use the powerful claws, so your blocking will be decent with a shield - and you can save the skill points put into Weapon Block for other skills like traps.  Dual wielding will become the novelty it is for Barbarians - fun to play that way, but not something you'd want to do in Hardcore mode or for ladder development.