1) The Story - apart from the Despicable Me movies, The Secret Life of Pets and Sing, Illumination's story problems plagued their live-action/animated hybrid Hop and their adaptation of Dr. Seuss' The Lorax. The story of Hop is a cookie-cutter 'rebelling against tradition' story with an abysmal twist on the Easter Bunny folklore the film is based on. This is just everything wrong with so many live-action/CGI hybrid movies. As for The Lorax, while not a bad film, it completely misses the point of what Dr. Seuss originally envisioned. Poorly developed story, one-dimensional characterization, forced gags, filler and outdated feature animation cliches completely rendered The Lorax a truly committee-driven animated mess. Even decent stuff like Sing and The Secret Life of Pets have some problems on their own, the former suffering from too much subplots and the latter misunderstanding the first Toy Story. So, if Illumination really wants to make a good animated movie for kids and families, they should rely on more experience and creative people with story writing skills. Take Ted Elliott, Terry Rossio, Joss Whedon, Bob Tzudiker, Noni White, Tab Murphy, Glenn Leopold, Sean Catherine Derek, Sherri Stoner, Deana Oliver, Philip LaZebnik, Nicholas Meyer, Sam Henderson, Pat Alee, Adam Beechen, J. Michael Strazynski and Michael Reaves for example. These are all people who have fantastic experience in animation writing. They can write a very good and engaging story for a modest-budgeted Illumination movie and the works of LAIKA proved it.
2) The Animation - even though Illumination produces low-budgeted animated movies and I have no problem with that, even a low-budgeted animated movie can be done the same way of Walt Disney, Don Bluth and Hayao Miyazaki: passion, heart and effort. These are the amazing three components for a beautifully animated movie regardless of its production cost. And Illumination only had all these three when they produced the original Despicable Me. It was the pet project of the amazing ex-Disney animator and artist Sergio Pablos and this film showed it. It wasn't a masterpiece, but it's simply Illumination's best work, because there was passion, heart and effort into it. After Pablos left Illumination, their animation style became dilluted. Their character designs took a nose dive in quality. Sure the original Despicable Me isn't beautifully animated, but their designs weren't that bad because they were courtesy of both Carter Goodrich and Sergio Pablos. It was in their following movies that the quality of their signature art style went completely lost. The humans and animals in these movies has so many exaggerated limbs and other features that they look like Frankenstein's disowned creatures. And the Minion designs are too generic and bland to be distinguishable from each other. On the top of that, the way the characters move is a far cry from everything other studios have often achieved and perfected and the fact that they reuse the same designs and models is the rock bottom. Why doesn't Illumination hire more creative and renowned artists like Dan Haskett, Jean Gillmore, Hans Bacher, Ruben Aquino, Mike Mignola, William Joyce and Brian Froud for their future material? These people could easy make a potential magnum opus for a company that's otherwise known for their Minions. Also, they could study Richard Williams' The Animators' Survival Kit to perfect their low-budgeted animation.
3) Minion Oversaturation - even though I like the Minions, I'll never forgive Illumination for being corrupted by the Frozen mania. They dropped the true heroes of the Despicable Me franchise and made the Minions the attention-whores of all Despicable Me release covers and merchandise despite being the deuteragonists. Not even Sing is safe from this sickening business practice as they ignored fan favorites like Johnny the Gorilla in favor of comedic tritagonist Gunther the Pig in merchandise of the film. So why don't they market all characters equally?
Overall, Illumination Entertainment is not Pixar and Studio Ghibli neither. But if they combined a solid story with appealing designs and perfected their low-budgeted animation by using the same models sparingly, they could have a more decent classic featuring characters we can connect to and scenes that would emotionally move audiences. Now that Illumination is now producing an animated Super Mario movie, they better not disappoint us or they'll make another disastrous misstep for animation. Illumination could be more than an executive-driven animation powerhouse by giving their creative talent more creative and artistic liberties and having the right people running the show. And that's final. Period.