The movies totally need to be G1 accurate! Because Barricade should look more like this...


And Blackout needs to look more like this:


G1 accuracy all tha way, bay-bee! #ruinedforever

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On a more serious note, I think that people will always compare adaptations of any material with the original source. However I think that most audiences are more forgiving and accepting of changes made to adaptations if it's actually good. An example are most of the movies based on Marvel Comic characters -- for the most part they are lauded by fans who have come to accept deviations from the original source. Wolverine shifted away from wearing yellow spandex to black leather and then to wearing whatever the damn hell he wants.

Having said that, I think that it's arguably important for adapted characters to at least retain some semblance to the core spirit of the character. Even Peter Cullen has criticised the way that Optimus Prime has been portrayed as a more ruthless character in the Movieverse (especially AoE) and hopes that future films will portray Prime more like his G1 counterpart (which the first movie actually did pretty well). Deadpool's first cinematic appearance was not popular with a lot of fans not just because he lacked the iconic costume, but moreso because he utterly lacked his trademark personality, which in the film he actually had before be became Deadpool. He was actually pretty good as Wade Wilson, the merc with the mouth... until Striker went and removed it. That just killed the character off. So I think one of the tricky things about rebooting or adapting a franchise is to try and strike that balance between bringing something new/fresh to the character but also trying to stay true to the core spirit of that character.

Optimus Prime from the first movie struck that balance pretty well IMO. He was true to his core G1 character in terms of being the heroic messiah-like saviour archetype... willing to sacrifice himself to destroy the AllSpark, and even when Sam pushed the Cube into Megatron's chest he shouted, "No, Sam!" and then lamented over the death of Megatron saying, "You left me no choice, brother." This exemplifies the deep spring of compassion that we know G1 Optimus Prime for. But the new element that the movie brought to Optimus Prime was that he was not hesitant to quickly dispense of Decepticon combatants in battle, such as the way that he beheaded Bonecrusher on the highway. This was not done out of malice, anger or vengeance, but out of necessity (the needs of the many outweigh the needs of the few). Bonecrusher's attack was threatening the lives of human civilians -- a whole bus load of people were already dead. Optimus Prime had no choice but to kill Bonecrusher in order to save human lives. A more G1-accurate Optimus Prime would have been more likely to abstain from finishing off Bonecrusher, allowing him to escape and endanger more lives. If you look at all the criticism that the first film received, nobody ever complains about the way that Optimus Prime was portrayed. Some people complain about his cosmetic looks, such as being a long nose truck or a Prime with chopper flames, but these are just superficial elements (much like Deadpool's costume). What really matters is his persona, which I think the first movie did pretty well (they kept it simple and it worked).