ODST has a good campaign overall, and it's final level is great, but it just feels very staggered and disjointed as far as the storytelling goes; due to the flashback sequences. I think they made a pretty bold statement with the game, and I like the film noir elements, new music and overall 'feel' of it, but elites were always more fun to fight than brutes and for a Legendary run specifically, it's a bit too easy and lacks the intensity of Halo 2 and CE.
Halo 3 has the worst campaign in the series in my opinion, just because there were so many missed opportunities as far as telling the story of the Separatists, Johnson's pointless death used just for emotional effect and despite the introduction of new flood forms, the flood levels are a real drag to play through; especially Cortana, which is horrible on Legendary.
Reach's campaign is ok, but it never felt like anything special to me. Some interesting level design in places, but again Legendary was fairly easy, apart from a few select fights and some awful vehicle parts (which always suck on Legendary because you're just a sitting duck). This is another reason for Halo 3's campaign not being fun on Legendary. It isn't hard overall, but because vehicles blow on Legendary, there being lots of vehicle battles makes it a pain to play through, combined with how irritating the Flood pure forms are, and the sheer amount of them through the campaign, it can be a horrible run.
I play everything - campaign, ranked, social, firefight, forge, so I don't think any playstyle is superior.