Well, at least in my view, this is where I don't mind artistic liberties being taken and seeing what new things a given iteration's production team can come up with, because... well, there's really nothing special about Ironhide's G1 design. The character hadn't been featured since G1, and his look is nowhere near as memorable as Prime, Bumblebee, Jazz, Starscream, Soundwave, etc... he's a boxy red van. That's it. The character was memorable because of his personality. He was a gruff veteran Autobot warrior always itching for a fight. So the movie team completely redesigned the character based on that personality. And while he looks nothing like he did 20 years prior (which, again, in my view, unlike characters like Optimus Prime, isn't really a problem), he now has a design that helps better convey the same personality of the character, along with some new distinctive features, like his cannons, which have become an Ironhide staple since. I think that freedom to experiment can often lead to new and better things, although I guess as someone who didn't grow up with G1, I don't hold a lot of that as sacred versus those who did. Maybe fans who grew up with G1 do consider Ironhide's design iconic, I just personally do not.