Compared to SM's last debut, Red Velvet didn't get much lead time before their major release -- SM Rookies promotions aside, they had just enough time for several teaser photos, a "Be Natural" cover by Seulgi and Irene, and one music video teaser. But I think this approach worked because it allows the finished product to speak for itself.
And speak it has. We get two very important pieces of information from the "Happiness" music video alone, information that can and will define Red Velvet as a group.
From details like the styling, the production quality of the song and video, the bombardment of colorful visuals to major decisions like the song choice, "Happiness" has SM all over it. The song is undeniably pop, and there are also hints of an f(x) influence because of the singing-talk at the verses, which fits it cohesively into the SM catalogue. The hook is ridiculously catchy and extremely easy to sing along to -- it's literally just "la la la"'s. Strong recall is a good quality to have in a debut single because that's step one of getting the group out there -- once people remember the song, more often than not they'll start remembering the group. And SM definitely knows a thing or two about strong hooks.
For me, I prefer this approach much more because the relative simplicity of the performance itself shows Red Velvet's capabilities and how comfortable they are on stage and it doesn't overestimate what they can do at the moment. They're not quite your perfectly polished SM performers technique-wise, their movements and stage presence could use some dimension and the choreography itself is loose and awkward. But they show the beginnings of an effortless conviction to their performances -- they're confident with what they're doing, so they're having fun and they know how to show it while still sticking to the set choreography.