There is character progression (not directly "levels" but gaining new powers and access to weapon tiers). There are instanced mission locations that require a group of characters rather than going solo. There are all the usual power types (tank/aggro, damage, debuffs, heals, etc) but no direct "healing class" or "debuff class". You could select your powers and item foci though to essentially make yourself a healer or debuff centered character for group play.
You can switch out powers pretty much on the fly so you can have a "group play" build for healing or tanking and another "solo play" build with more rounded powers.