Both movies summarize their respective TV series. They are made around the same period, and have similar art and animation. Both focus on intense battles between mecha, and also have some romantic elements (which are more highlighted in Macross). Both have an overall similar vibe, with the main difference being that Gundam is a bit more mature, while Macross focuses a lot on music.
Both are the second films in their respective film series that summarize and retell the events from the TV series. Both are mecha anime, featuring a young protagonist who has to pilot a mecha and experience war at a very young age.
Both are military science fiction anime that focus on a conflict between two factions that share different ideologies. Both series portray war in a fairly realistic way, showing its destructive effects, as well as having many characters die in the line of duty.
Both are mecha anime, which try to deconstruct their genre. In both anime, the main protagonist is a teenager, who becomes a mecha pilot, this becoming a child soldier in a devastating war. Both anime show the impact of war on these children, as they are forced to kill enemies and cope with the loss of their comrades. Also, in both shows, the main protagonists have a similar attitude and often refuse to participate in combat. Overall, both anime have a similar grim atmosphere and deal with similar themes.
Will someone PLEASE think of the children?? if u put away the extraterrestial storyline of Layzner, it pretty much comes down as kids in warfare that survive by the skin of their teeth, both refer that! with mecha and all!