I emerged heroes3 and it installed lots of data files to /opt/heroes3. It should be in /usr/share or /var or something. Never /opt! Reproducible: Always Steps to Reproduce: 1. 2. 3.
That's where binary packages are installed on Gentoo. You have the option of setting GAMES_PREFIX_OPT if you prefer a different location. Only do that if you know what you're doing though. You'll probably need to pick up the pieces if something breaks because of some odd setting.