Spoiler-free review of season 1
Review in brief:
K-On!'s 1st season cemented much of what are now seen as the quintessential elements of the CGDCT subgenre. Rather than bring anything new to the table, K-On! distilled what had already been done into something that's easy to relate to without sacrificing much in the way of characterization, comedy, and plain old fun.
Review in full:
K-On, like most of what is found in the CGDCT (Cute Girls Doing Cute Things) subgenre, isn't really about anything. Sure, there's themes that are lightly touched on, and sometimes they play music, but the story isn't the main point. K-On is far from the first CGDCT anime to come about and was hardly an innovator in its field. That distinction is generally given to Azumanga Daioh, whose blend of loose (often to the point of being surreal) comedy and iyashikei (healing) undertones set a precedent that has largely remained followed since it started as a manga 20 years ago. Aside from being much less surreal, K-On!'s style is fairly standard even for its time, much more so these days when it's been done multiple times per season for years.
Yet K-On! is a much beloved anime and a worthwhile entry point into its subgenre to this day. This season may not stand out against many of its peers, but it provides a lighthearted, friendly experience and it does this especially consistently. K-On! not having much of a focal point actually plays to its benefit, as it allows the anime to take full advantage of its simplicity. Sure, it lacks the narrative depth you'd expect from something more focused on its plot, but K-On! isn't as shallow as it looks and goes as deep as it needs to for it to provide an all-around fun time.
What Yui imagines the Keion-bu is like before joining. Add some friends and replace the castanets with tea and it's not that far off.
Rather than try and compose anything poignant or grandiose, K-On! simply tries to bring about a smile through its calming normalcy and general goofiness. It does a splendid job of capturing the air of an after-school club with close friends, often subject to goofing off and enjoying each other's company rather than focus on just the club activity which, while a shared interest, is but a single facet in the relationships of its members. Virtually anyone who has been part of a close group of friends can relate to it, and those who haven't can easily get an understanding of what would make such an arrangement a fun and worthwhile venture.
Since we've established that the "cute things" being done aren't the important part, it's the "cute girls" that are the main appeal. Of course they're visually cute, but this isn't an ecchi title and the resulting innocent nature of the anime is part of the charm. No, it's the selection of cute personalities playing off each other that's important. The quirky but rarely over-the-top bunch of goofballs in K-On! definitely get the job done. Sure they're initially defined by a handful of personality traits, but most of the cast supplement each other's quirks over the course of the season, allowing them to flesh out quite nicely and even lightly develop.
For instance, Mio has stage fright and doesn't like costumes, but there's some costumes she dislikes more than others and the difference between performing for her friends versus the whole school is clear. From there, K-On! builds on those traits by having her become accustomed to the outfits that she dislikes less and find reasons to slowly embrace her creative side and worry less about sharing it. It's not a big development, and it's been done countless times, but the slight drama that brings it to light and the subtle shift in how the comedy plays off of these developed traits goes a long way in keeping the humor from getting stale and making the moeblobs the show starts with into a fairly convincing group of friends.
Sometimes season 1 looks really nice, but there were definitely some corners cut.
Speaking of moeblobs, they come up visually quite often in season 1. K-On! wasn't the KyoAni goldmine it's known as today until after the anime was airing. While KyoAni didn't give K-On!'s visuals the same effort as their more serious prior works (such as their Key adaptations) they still put more into it than the standard CGDCT usually receives even now. On those infrequent occasions the characters actually perform or otherwise take their club seriously, K-On! features some nice animation. These moments are rather smooth, lively, and feature enough intricate detail for nice touches like the music being played and the animation for the girls playing instruments lining up just about perfectly. On the other side of the coin, comedy moments often heavily simplify visual details and have much less animation, especially when it comes to the girls and their faces. At least the framing and background art are always of a high quality to make up for those scenes when they occur.
Fortunately, the sound quality is more consistent than both the animation quality and the Keion-bu's focus on music. Sure, the performed music is mostly J-pop, but it's noticeably spirited and sounds like the sort of thing a bunch of high-school girls would come up with (save for the ED, which appears much more professional as if to show the club's potential). The background music is light, simple, and less poppy, but it fits the setting, contrasts the performances well, and is quite varied overall. However, the voicework (Japanese dub) is where K-On's audio truly shines. The girls all receive expressive, distinct, wide-ranging voices that fit them like gloves. It makes them feel so much more alive that K-On simply would not be the same without its voices.
Like most CGDCT anime, K-On!'s 1st season is simple and largely uneventful. All it wants the viewer to do is have some fun, and enough of an effort is put into delivering relatable & organic fun for it to accomplish that consistently. It's that consistency that makes this season a good entry point into CGDCT, because you'll definitely know what it is by the last episode and can easily make a judgment as to whether it's for you or not from there. This season isn't particularly memorable, but for what it is there's little to fault it for, and consistent lighthearted fun has its value.