So far I've only played the mage (I only control my party members under extreme circumstances).
Like most games, the mage is extremely underwhelming at starter levels (believe me, a chunk of the game had me bored with my character in combat). But once higher levels are attained (and your companions skills/abilities improve along with yours), the class actually gets much better.
I play him as a support character, casting barriers for my frontliners (Blackwall and Iron Bull) while shocking them as barrier recharges. This game has actually made ranged characters feel more viable, so I can imagine archery rogues aren't so bad.
Have yet to try out the other classes (kind of just sticking with one character for an entire playthrough. Eventually I'll have a character for each class/fighting style). Dagger rogues with a subterfuge/saboteur style build seem like fun as do archers. Not too keen on two hand warriors and it kind of stinks you don't get shield bash early (my main draw to the sns warrior).