Thus far, the only real drawback present in Marvel's Runaways is the way some of the props and visual effects clash with either each other, or the setting they're in.
Runaways exists in a peculiar gray area between the more realism-based MCU Netflix series, and the more sci-fi heavy realms of Agents of S.H.I.E.L.D. and Inhumans. In turn, a lot of the outlandish props, such as the X-ray goggles, feel out of place in the otherwise down-to-earth Los Angeles setting. To an extent, that was probably part of the idea to show how out of their element the characters are, but it can still be rather distracting at times.
In addition, some of the CGI effects are more believable than others. For instance, Karolina's glowing skin looks fantastic, but the same can't really be said for Molly's glowing eyes. And the convincingness of the Yorkes family's dinosaur varies from scene to scene.
In short, the visuals in Runaways are a mixed bag. They did their best considering the TV budget they had to work with, but not all the visuals shine through.
With that out of the way, however, let's get to the ups.