Just Kinda Bad
Return to Ostagar is a disappointing piece of content when compared to the two previous packs (Stone Prisoner and Wardens Keep). Adding just one new area and loot that seems to not scale. This means that i would be only really be able to recommend the pack to perfectionists.
However, the DLC does have some redeeming factors, including some new party dialogue that reflects on King Cailan and Ostagar and the ability to see the aftermath of a Darkspawn raid.
I would suggest that if you buy Return to Ostagar, then you should start the quest around Level 8 to 10
Note: this pack was played with a Level 25 Dalish Rogue and that may colour my judgement.