I found my marauder was like this through leveling. oh wow i am strong! after lvl 23 or so, omg i am so weak!, hit 35-40 oh yah im strong and uber again look at me, 45-50 *** weak again nooooooooooo. hit 50 ran dailies got the gear up back on top baby!!!
the class is very "hands on" takes getting used to tough to play harder to master. i switched spec while leveling i was carnage at first then tried annihilation which i wasnt keen on at first cause im not a DoT type person. but the way they made it for DoTs is so simple and awesome you get the hang of it right away.