This question... oh boy
Zimmer is a film composer, and that should say it all. There is 2 types of film composers, a) the classically / formally trained ones, and b) the guitar player (or something else) turned film composer.
Zimmer is not a classically / formally trained composer, so it is not fair to look at his of work like someone would look at scores from Steiner, Korngold, Goldsmith, or Williams. I will not look at Zimmer's scores to 'learn' composition. Imo, he's the perfect example of the 'modern' film composer writing in a simple style (can't expect composition complexity like the names mentioned above) and presenting it in the highest possible production value. And for that production value / sound he's a master. Everyone tries to mimic the Zimmer 'sound' one way or the other, listen to most of the trailers out there... look at most of the scores on movies today, everything is almost the same
Zimmer is responsible for many composers working today in Hollywood. Too many to name here have come out of the Remote Control and so on set-up. Even musicians / performers on his scores have started careers as film composers pushed by him. Most of these composers, with a couple of exceptions (John Powell comes to mind,) write like Zimmer. And that does amplify even more the Zimmer 'sound.'
Zimmer is a successful businessman. He found a formula, built a functioning system, and is now worth millions doing something that others try learn how to do for decades in schools like Julliard, McGill, etc. To some he maybe a 'genius' composer, to some, his mediocrity has become a style and the norm of the day.
Zimmer is a master dramatist and for a film composer this is absolutely a necessity.
Regardless of his writing style, or how he's done the scores we hear today bearing his name, Zimmer is an authority and a huge reference for a lot of film composers or want-to-be film composers out there.
Imo, Zimmer, or anyone for that matter, should be seen for what they are. A comparison with a titan, such as, John Williams for example is not fair
There is room for everyone in this business