Grojband is one of those cartoons that make you laugh or giggle for all the right reasons. The writers, given that each "episode" is normally 10-12 minutes long, do an excellent job of pacing and keeping the humor & story consistent while maintaining the characters well.
Here are the some main characters of Grojband as summarized simply enough by me:
With the way the usual boy punk rocker is written in mainstream media, seeing Corey was a breath of fresh air. The writers play on that archetype by making him oblivious yet radical & friendly at the same time by putting in jokes that play off that characterization well. He and Trina (older sis) do not get along at all. Trina might as well be the definition of selfishness, egotistical, and malicious but Corey always seems to find his way.
Kin and Kon's (twins) relationship as the "nerdy engineer keyboard player" and the "not as smart gentle giant drummer" are surprisingly not cringe-worthy as we see that Kin (smart) never looks down on Kon or his friends. They have a healthy brotherly relationship and are literally true bros.
Laney, as the only female in the band, comes off as someone who really doesn't mind being the only girl. She's shown to be just like her band mates (save, for an obvious crush on Corey shown in some episodes). She's shown to dislike all that is traditionally girly but it isn't overplayed to a tiresome point.
The animation is great, in which it doesn't make out each figure to be a stiff puppet with annoying voices (ex. Johnny Test). The movements are perceptively smooth and every character has their own shapely & diverse quality to them. The music is done well enough to keep the tone appropriate throughout the episodes. I noticed that the final songs in the end of each episode (when Corey gets the lyrics from Trina) explore different genres of music yet maintain Grojband's rock attitude. I find that SO refreshing. As far as realism goes, cartoons don't always have to be constrained to our world's realistic values and physics. When you claim that a cartoon such as this isn't realistic enough, you've gone and overlooked every component of the cartoon and labeled it as "not good enough" through your own blind observation. It's ignorant and you're literally missing the whole point, but if that is one's opinion then one is welcome to uphold whatever they believe.
Overall, it's a well-maintained show that plays on certain archetypes and over done subjects to create something entirely refreshing and humorous to both kids and an older audience alike. It's cute, silly, and while it's not the most visually stunning cartoon, its substance is well worth the short amount of time each episode has.