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Is combat in DCUO, well...difficult? I'm generally not much of a fan of action combat, but I feel the pull of a super hero MMO.
"I don't give a sh*t what other people say. I play what I like and I'll pay to do it too!" - SerialMMOist
"If I offended you, you needed it" -Corey Taylor
Combos are done with the mouse. They mix both buttons and series of "click" and "tap" (click left + click right, click left + click left + tap right, etc). Each weapon has it is own skills, and each skill its own combo.
It reminds me old console games in that way. If you are accustomed to console game-pads, it is better you play with it.
I tried it several times and the combat was too weird for me. Then I tried it again recently, it finally clicked and I really loved it.
I can't think of any other MMO which uses mouse combos like DCUO so it really does require a mental shift. That said most of the content (at least pre-end-game) is quite easy and you don't have to use combos.
You can specifically choose equipment which boosts ability (i.e. executed from hotbar like other MMOs) damage or weapon damage. So you can diminish the important of combos in that way.
There are some differences between power sets.
Light has its own built in (simple) mouse combos which you can use instead of or in addition to weapon combos. I really like them. It's one of my favourite power sets.
Celestial also has its own built in mouse combos but they're a bit more complicated.
Rage also has some built in mouse combos but I think fewer than Light and Celestial.
Nature has one shapeshift form (canine) which completely rules out weapon combos. That form has abilities you execute from the hotbar and you regenerate power more quickly while in that form. So as a dog you could ignore weapon combos.
That said the weapon combos are pretty easy once you get used them and your fingers will just do them naturally. They are quite different across weapons though, so once you settle on one you like stick with that one as much as possible.