Marauder seems to be much more DD orientated than it is Tank orientated. It can probably be a nice back-up tank, or a small group tank just fine.
Pugilist seems to be split down the middle on the DD/Tank scale. It gets access to a lot of evasion, enmity and stun abilities on the way to 50.
You can definitely make it a DD with a different choice of abilities though.
Lancer seems to be like Dancer in FFXI, only, it's more capable of dealing damage. It has quite a few abilities that enhance fellow melee classes.
Archer, like said previously, is pure DD as far as I can tell.
Also, expect new classes in future updates.
Edited, Oct 4th 2010 12:58am by Kirby