Iron Man 3 had an epic finale. Throughout the film, there were subtle hints toward something Tony had prepared called the "Iron Legion Protocol," and it was revealed for the third act in an epic way. When it seemed that all Tony and Rhodey had to take on Aldrich Killian and his Extremis army was each other and a gun, in flew 34 Iron Man suits. Each had a unique design and color scheme, and some were even designed for unique purposes.
Unfortunately, due to the nature of Iron Man 3 as a relatively standalone blockbuster, the specific purpose and function of each suit were not explored in the film. And by the film's end, every single Iron Man armor was destroyed. This is an incredible shame because the production team put an outstanding amount of effort into the design of each suit of armor that makes up the Iron Legion in Iron Man 3. They even gave most of the suits names.
The Iron Legion in Iron Man 3 was criminally underused, and, unfortunately, the concept was never revisited in quite the same way in the Marvel Cinematic Universe. With over 30 different variations of the now-familiar Iron Man armor, it's an impressive feat to have so many unique versions that are fairly easy to identify on-screen. It's an extremely fun final battle, with Tony running and jumping from suit to suit as he keeps trying to go toe to toe with the Extremis soldiers.
However, in order to appreciate these suits with any level of depth, one has to do their own research and reading. While omitting this information encourages fans to engage with the movie's supplementary materials, it provides an increased level of depth that would have been appreciated in the film itself. The suits are designed with specific purposes in mind, but these are never displayed on screen. "Heartbreaker" has a larger than normal arc reactor, but it's never used as an attack. "Shotgun" is designed to go Mach 5, but audiences never see it break the sound barrier. "Starboost" is designed for sub-orbital space travel, but audiences never see it leave Earth's atmosphere. Understandably, allowing these suits to fulfill their function would've required drastically reworking the finale, and that wouldn't have been easy to do.
Furthermore, in subsequent appearances in films such as Avengers: Age of Ultron, the Iron Legion is not an army of unique and individual Iron Man suits, instead of being a series of identical unmanned drones. They look basic and uniform in this film and don't have the flair of the Iron Legion from Iron Man 3. From a storytelling perspective, it makes sense; the Iron Legion drones in Age of Ultron provide a blank slate for the Ultron A.I. to imprint itself onto. But it means that the legacy of the Iron Legion in the MCU does not leave much of an impact.
Perhaps in the vast multiverse, there is another world where the Iron Legion from Iron Man 3 made more than one film appearance, a world where they reached their full potential on the big screen. As it stands, their full potential is left to the imagination of fans -- which, in all fairness, is not the worst place for it to be.