Personally as someone who hated tanking in say, WoW and found it quite stressful, so far tanking in Swtor has been fine, fun even on my Juggernaut gradually getting more and more abilities and I've been leveling as Immortal spec so getting to know everything as I go, certainly helps with all the heroic missions. Thinking of trying Vanguard or Shadow too for a different style.
Second boss encounter on Mandolorian Raiders was pretty tough and my Athiss group contained a Mercenary who kept pulling before me or using Death from Above on a group of elites/strongs to pull and moaning that I couldn't get aggro on them all quickly (pre-threatening scream aoe taunt), but overall enjoying it a lot.