Let us look over some of the facts about Assassins, and why many people hate/love them.
Hate:
1. Assassins die too much.
-They do? How can this be possible when it is so easy to put something like critical defenses, flashing blades, mystic regen, or even earth armor spells into a build? Newer players die all the time with assassins sure, but most of the times they have like 7 attack skills and shadow refuge. I've found in nearly any situation any one of the above skills can easily prevent masses of death in even the most elite areas. Then add skills from secondary professions to increase this ability in many more ways as well.
2. Assassins have 70 defense.
-So having -10 AL from the maximum is bad? Check out the inscriptions! Every one of them provides between 10-20 armor to certain areas, or a full 15 while attacking. Add one armor skill to that and you far surpass a warrior! On top of that, 75% blocking skills are very common in assassin builds, as they have more of them than any other, except perhaps the ranger. Assassins are however, the only profession who can keep them up constantly with only one skill.
3. Assassins can't do anything but teleport around.
-Ah so thats why is the #1 skill used by x/A players a shadow step? Other than necromancers(which need corpses) and Ride the Lightning(l0l) Asssassins are the only class capable of moving instantly to an enemy, and with great effect. And trust me, assassins can do MUCH more than just teleport.

Thats a FEW of the many reasons people say they hate us... But now lets look at some points the good side shall we?
1. Speed.
-"OMG what just happened?!?" This is what I commonly hear in PvP a few seconds after I target someone. Assassins have by far the highest killing speed of any profession in the game. In PvP a sin can stop you in your tracks, teleport to your exact location, lay down about 500+ armor ignoring damage, and apply several very harmful conditions, all in less than 2 seconds. In PvE, with enemies who are normally exceedingly weaker than human powers, an assassin can clear mobs with rates near to nukers. Skills such as Assassins Promise, Death Blossom/Moebius Strike, and run boosts put them among the quickest killers anywhere in the game.
2. Survivability.
-Yep, I said it. Assassins can survive amongst rampaging monsters and such. Personally I always carry defensive skills in my sin builds, and I usually have constant 75% blocking to nearly eliminate Melee damage. Assassins are the only classes able to do this constantly with only one skill(and several skills work for this). While elemental damage can be a problem, most assassin heals can more than cover for it. Even Shadow Refuge every few seconds will heal a considerable amount more than most people think. Way of Perfection with critical hits is another great heal. When healing isn't enough(in many cases it isn't) thats where shadow stepping comes in! Not only is it a great way to surprise enemies in PvP, but the best possible way to get OUT of a battle when things turn bad in PvE! On top of all of this throw in assassins various stances and enchantments for protection, as well as conditions such as Daze and Blind to shut down nearly any enemy. Thats not even getting into a secondary profession!
Oh yea almost forgot, its the only profession with a skill that more or less says: You are invincible for 5..20 seconds.
3. FUN!
-Nothing in this game is more fun than taking an assassin and jumping from target to target killing off enemies one at a time in rapid succession. After 6 months of playing, I have never had more fun with any other profession, or any other types of builds, than a pure assassin.
Thats a little bit about them, but if you ever play one for yourself and become successful at it, you'll quickly realize why so many have chosen to move to the assassin profession.
My theory: Assassins are not properly used much of the time. When assassins first came out, people became crazy to try them. Alot of new players wanted to be a cool assassin ninja kind of character, but really had no idea how to play them. Many assassins these days still aren't sure how to effectively use this profession, and over the months players have died and been unable to kill enemies well enough to compete with other professions. Thus, assassins began to gain a bad reputation as a "noob class". Sort of a class where all the new people wanted to go to seem cooler and stronger, but they really didn't know how. Overall, assassins are not a very easy class to use. Unlike warriors and elementalists where its either load on defense and smack enemies or load on huge firepower to blow things up, assassins require A LOT of strategy to use effectively.
My solution: Learn the basics before you start one. Assassin's are probably not the best idea for a first profession(even though I did

Ok, my rants over for today. Comment/rant/spam/flame/laugh/talk/whateverotherwordsyoucanthinkof away!