I know there are plently of QQ reviews about Guardians but I just wanted to share mine as well and I am going to keep it really short;
I've mained Mesmer, to be honest, I do not have any problem with dealing a Guardian. If I take right actions like dodging skills or using right skills in right time etc. I can take down any class. I believe that mastering any class and playing it is the right the key. But, the thing i want to mention is that the attention you have to pay.
For example; as a Mesmer, I have to calculate every move. I cannot use my skills randomly, I need to use them in a correct situation. To success, I have to play smart.
And about Guardian; I just started to play with Guardian a few days ago. I just checked a meta build and never watched a single PvP guide. What I do is just laying down whatever trap I, and spaming F2 F3 and Sword 5 when I am low. I don't even select a target, I just push the buttons and try to survive while laying traps around. I have more win ratio than any other class now.
I am not trying to tell that Guardian's damage should be nerfed, I just wanted to point that Guardians shouldn't be a class that is really easy to play.