CoO is widely known as the worst story campaign parts, including the planet and infinite forest - good concept, poorly executed.
Warming is something they realised had to better and was. Story has always been shortish compared to overall content they offer. They brought alot in that one though, some really good exotics to chase and secrets to find.
Whilst CoO story was poor, dont forget the grind for Osiris weapons. A few are really decent and Saint-14 quest was pretty special and cool to run through which drops around 5 weapons into the CoO weapon grind (Saint-14, one of the most known Titans in Destiny Lore, you know the one with the Helm of Saint-14 helmet that blinds enemies in a Titan Bubble super? that one). His Shotgun as the reward is a good one to own and use in PvP.