Mobile Suit Gundam I, Evangelion: 1.0 You Are (Not) Alone Recommendations
Both of these films summarize the events of the early episodes in their respective series. Also, both of them feature a young pilot who has to pilot a mecha for the first time and is learning how to cope with that experience.
Both of these are the beginning film of the condensed version of the original series (keep in mind that that doesn't mean that its a recap like Evangelion: Death and Rebirth. You can still watch these with the confidence of having the original integrity of the story).
Both are famous for not only its impact on mecha, but for anime in general. Although Evangelion (especially since 1.0 is a revamp) has better animation and is known to have a darker atmosphere, MSG is well respected for its great character development and plot.