In the future mankind has expanded into space with humanity now living on both Earth as well as self-contained colonies in space. Eventually several of these colonies form the Principality of Zeon and succeed from the Earth Federation leading to war. On Earth Federation colony, Side 7, a surprise attack is lead by Zeon forces who are targeting both the warship White Base, and the newly developed mobile suit, Gundam. A teenager named Amuro Ray stumbles upon the Gundam during the siege and out of desperation boards it and against all odds manages to hold off the Zeon forces long enough for White Base to evacuate. Amuro now finds himself embroiled in the conflict between Zeon and the Federation reluctantly piloting the Gundam for the Federation and often squaring off against Zeon's best mobile suit pilot, Char Aznable also known as The Red Comet.
In the past 40 years since the first Gundam series graced airwaves in 1979, Mobile Suit Gundam has become not only one of the most recognized "giant robot anime" ever made, but also one of the most recognized media franchises spread across TV, OVAs, video-games, manga, models, and even a forthcoming live-action film, but that almost didn't happen. Ratings for the original series were so poor that the show's sponsors, now defunct toy company Clover, cut the episode order from 52 to 39 with staff able to negotiate an extension for 43. After Clover cut ties with the series, Bandai acquired the rights and with their release of models the series popularity soared giving second life to the series and spurring the creation of three compilation films retelling the story. Series wrtier/director Yoshiyuki Tomino took the concept of "power armor" found in the novel Starship Troopers and mixed this concept with traditional tropes of giant robot anime and manga to tell a story about war making Gundam the earliest examples of the Real Robot genre where giant robots are more grounded in terms of how they're utilized and operate forgoing the more over the top Super Robot elements seen in things like Giant Robo. Following the renewed success of Gundam, Tomino revisited the series by recombining footage into a trilogy of feature films which became massively popular to the point crowd control measures were implemented due to the large crowds drawn by the first film with grosses for the films only growing with each subsequent installment. In terms of the first Gundam series, this is probably Tomino's definitive version of the story, but it's inescapable that it feels like a series of episodes daisy chained together.
In terms of getting across the story beats, the movie does it well with clear establishment of characterization with Amuro Ray's reluctant hero who's world is shaken when he becomes a reluctant participant in a war with very clouded motivations (which is to be expected as we're experiencing his exposure to the conflict primarily from Amuro's viewpoint). The movie creates a world where all the key military personnel on board the White Base are all either very old or very young giving the impression of a world where the most able have been lost to this widespread conflict. There's also other plot threads such as character Sayla Mass and her set-up familial ties with Char Aznable which in turn leads to Char's ties with the ruling Zabi family of Zeon. The plot threads are engaging and keep you interested, but since this story was originally told in the format of a TV series, the movie feels like a TV series with really no sense of finality to so it really doesn't stand on its own as a film (at least individually).
If you are curious at checking out the original series, the Mobile Suit Gundam trilogy is probably the most convenient and polished way to do so. While the movie is pretty obvious in how it's scrounged together from episodes of the original TV show, it's about as well as one could expect given the circumstances, and the movie's themes of war and its wide reaching consequences and inherent shades of grey are well conveyed to the audience.
