Mages in 4e are actually not pathetic at low level; in general, the designers made a strong effort to keep classes balanced and effective from top to bottom. Most of the time, it worked.
However, I do think that in general some classes are harder to play than others, which I think is relevant to your question. I've bolded the classes that appear in the original Players Handbook, since I'm not sure what source you're using.
Easy: ranger, sorcerer, avenger, barbarian. These are all sort of point and shoot classes; you choose a target, you do your damage.
Simple: warlock, cleric, warlord, druid, invoker, warden, monk, psion, seeker, assassin. We see a few more damage-oriented classes here, but these have more choices to make. For example, the assassin has to decide when to use his shrouds for additional damage. I've also included a few control-oriented classes; the druid can be played as a damage-dealer with some additional control effects, and the invoker is similar in that regard. Finally, the warden is probably the easiest defender to play, because he can use his ability to mark everything around him for free. Again, fewer choices than other defenders.
The warlord and the cleric are leaders, or healers; I think to get the most out of them, it's a bit harder, but you can certainly play them simply. And minimaxing is not always the point of the game.
More complex: rogue, fighter, paladin, wizard, bard, shaman, ardent, battlemind. I consider leaders to be fairly tricky because you need to make good decisions about when to heal. The wizard has so many control effects you need to think harder about when to use them. Finally, the remaining defenders (fighter, warlord, and battlemind) have lots of decisions about who to mark and how to control marked enemies.
If I was going to call any of those really complex, it'd be the shaman, since you need to think about both the character and the location of the spirit companion you summon.
Big disclaimer: this ranking may change with the new builds available in Essentials this fall.