Disclaimer: english is not my native speaking, so bear with me, please.
There is one reason I see the smuggler COULD be the last played class. As I do play the Gunslinger I will just speak of it.
First: I do want to say, that it does NOT come down to to many buttons. but to many buttons you have to use within your standard priority system beside using cover (which does also need an extra easily reachable button, but does also bring in some other issues you have to care for) and managing your ressource just to do damage. We are not speaking of utility skills here (also some of those have to be used on a regular basis). Take also into account, that if you are playing especially Saboteur or Dirty Fighting, you do also have to take care of even more buttons because you will have to use some cover only shots beside your out of cover shots which do not get replaced once you are in cover. Because of that the cover-system of the gunslinger is different to a stealth bar (you won´t normally use normal skills once you are in cover).
In short, the smuggler (read gunslinger, see above) is too complicated because of too many buttons just to do you regular dmg. If some of you disagree I tell you to play a Sage instead and come back (the difficulty of a sage is different, because there are spells you do use for example to offheal - even as DD, but that is a totally different kind of complexity, because first you do have to decide to do further dmg or heal instead, those extra buttons won´t make your dmg priority system harder).
I hear some of you cry, but before I do come up with an (hopefully easy) solution, let me explain my opinion.
If one class is harder to play than another you do have a balancing problem. Take a look at pvp: If you have to manage (just a simple example, don´t read to much into it) 7 things when your enemy just have to manage 3 - both players skilled equally: Who do you believe will win? (I do also believe, that this is one reason Guild Wars seems to be better suited to structured pvp than WoW for example - but that´s just an uninformed opinion, I never played GW, just heard and read much of it).
It does transfer to pve, too. At one point equally skilled players will be traded differently because the difficulty of the encounter on top of the class will make a difference between a harder and a easier played class.
Possible solution: Do not make cover only shots, but make the shots better once the gunslinger uses cover. That way there won´t be even more skills on your bar once you have to take cover.