Really the two best mods are probably Rome Total Realism and Europa Barbarorum. Personally I play RTR, but that's because I have a few friends who also play and we have a hot-seat campaign that we're all involved in together. It plays slow, but it's still quite rewarding. If we could get the hotseat script to work in EB we might play that instead. I'm not sure though, that would probably slow things down even more.