Performance Issues
We have the benefit of foresight of knowing that Eternals wasn’t the best MCU movie of all time. This is somewhat supported by the fact that the film received a lukewarm 47% rating on Rotten Tomatoes, not that that means much. But when Iron Man 3 hit the theaters, people released a collective groan about it being the worst MCU film of all time.
That’s not to say that Iron Man 3 didn’t have its shining moments. For instance, do you remember how long it took for Tony’s armor to come after summoning it? That look of agony on Tony’s face while he waits for much longer than normal is pure gold.