Sonic Rainboom is one of the more popular episodes of the show, often remembered especially for the sequence at the end with the titular boom. While there is certainly a lot to like here, the episode is not as bulletproof as its popularity suggests.
From a visual standpoint, this episode does contain much of what makes the show look great. Movement is smooth and detailed, and the general designs are visually appealing as is typical. However, a brief few moments do look a little weird, but still with far less frequency than the early season. While more specific visual elements are designed well, the general look of the city of Cloudsdale is unfortunately a bit drab. The colour palette doesn't show much variation, and aside from the stadium the city consists mainly of a couple rooms and a handful of Greek-style houses on clouds.
The writing, meanwhile, doesn't contain the big laughs of several previous episodes, though Sonic Rainboom is still reasonably entertaining for the quick pace with which it progresses. The episode's attempts at humour mainly come from mild bits of silliness, and after "Feeling Pinkie Keen" they don't quite hold up as well. Still, the well-known cold opening is every bit as entertaining as it was the first time I saw it, and remains an iconic moment.
The episode attempts to have a stronger focus on character, with limited results. Rainbow Dash, in particular, is shown getting over her stage fright, but her internal conflict doesn't truly reach the forefront until halfway through, when the episode turns its attention away from world building and getting from place A to place B. It's at this point that the episode picks up, and showing Rainbow Dash's insecurities from under her outward bravado lends a bit more depth to her character, if not a complex sort of depth. Having to overcome those fears in order to save her friend is a nice touch, and that final sequence is still exciting.
On the other hand, the episode doesn't have much concern with the other characters. Rarity and Fluttershy are the two that have the second-most prominence, with Rarity exhibiting some of her worse qualities and Fluttershy simply being cute. The softness of Fluttershy's vocal inflections is of course a very cute thing. This is the first major occurrence of the "assertiveness" subplot for Fluttershy, which for some reason the writers enjoy rehashing. Fluttershy has her own minor arc in the intensity of her cheering, though repeated watching may have dulled its impact for me.
The writing is all very amiable, though it lacks some of the cleverness seen in the show's best episodes. Meanwhile, characterization is good, but not great, and a slight feeling of stagnation is setting in. It's an episode that doesn't take many risks, and it suffers for that. Still, there's entertainment to be found here, and for those who enjoy this show as breezy, light entertainment, it's an episode that clearly shows that. It's far from a bad episode, and it doesn't break the winning streak of this part of the season.