i am a gadgeteer and i had no probs. If you are a range class..just run around and spam skills + heal/mana.
Not thaaat hard. When i compare this to my first endboss fight in diablo..i had a hard time there too
(first char without cow quest hardcore lvl) but i did this solo too after some runs.

It depends on your tactic + build.

the good thing as a gadgeteer is that i have homing missle bullets xD
(like the amazon girl from diablo) so i just need to wait unti the boss is down + i use some granates or mines.
My build is pure marksman with some skills from the mine/trap tree