So a thing i think would make infantry combat much more interesting would be special, highly expensive helmet addons which would give you thermal, night, telescopic, x-ray, etc. vision. (But only close up to stop it from being too OP)
As a example: You are on a old, abandoned, huge flagship. There are no lights.. You know that there is a enemy somewhere, hiding. To find him, you use night vision, easily spot him and kill him.