This game has an amazing cast of voice actors. I will list what other game/anime each voice actor has been in, and that should be enough to explain how awesome the cast is:
Heroines:
Momoyo: Sakaki (Azumanga), Rider (F/SN), Tsugumi (Ever17)
Kazuko (Wanko): Nagamine (Seinarukana), Seira (Chaos Head)
Miyako: Oumi (Saya no Uta), Shirayuki (Sispuri), Putina (Osadai)
Yukie: Riannon (Tears to Tiara), Ririko (Sharin), Mikuru (Haruhi)
Chris: Tama-Nee (To Heart2), Hinagiku (Hayate), Akiha (Tsukihime)
Male characters:
Capt (leader): Kamina (Gurren Lagenn), Ishida (Bamboo Blade), Ein (Katahane)
Gakuto (buff guy): Trunks (DBZ), Mao (Code Geass), Dororo (Keroro Gunsou)
Moro (gloomy guy): Hidemi (Host Club), Shin (Gundam Seed Destiny)
Cookie (robot): Shinji (Eva), Maou (G-Sen), Lulouche (Code Geass)
Tadakatsu (Tsundere): Archer (F/SN), Greed (FMA)
Ikurou (pervert): Tomoki (Cross Channel), Inuyasha, L (Death Note)
Suguru (otaku): Kamille (Z Gundam), Lumiale (Angelique)
Kuki (rich guy): Tomoya (Clannad), Alto (Macross), Graham (Gundam 00)
Jun (bald lolicon): Kyon (Haruhi), Yuuichi (Kanon), Reiji (Kojika)
Kyojin (teacher): Nero (Tsukihime), Kotomine (F/SN)
Maro (weird teacher): Koizumi (Haruhi), Battler (Umineko), Yukito (Air)
Prime Minister: Houzuki (Sharin), Hiroshi (Kazokei), Cell (DBZ)
Frank (Chris’s dad): Char (Gundam), Shanks (One Piece), Gilbert (Gundam Seed Destiny)
Female sub-characters:
Chika (classmate): Sachi (Sharin), Mayu (ONE)
Mayo (loli classmate): Sayaka (Paniponi), Akira (Yosuga no Sora)
Umeko (teacher): Tsunade (Naruto), Sailor Neptune, Reccoa (Z gundam)
Koyuki (weird girl): Taeko (Swan Song), Aoba (Kazokei), Tama (Muv-Luv)
Margit (army girl): Haru (G-Senjou), Chie-Nee (Kira Kira) Kia (Inganock)
Kokoro: Akane (Muv-Luv), Len (Melty Blood), Miyako (Hidamari Sketch)