From: GANON1025 | #009
OK, then assuming I only have the red box what essential books should I look for?
'All of them except four or five' is the honest answer. For a slightly less expensive answer, PHB1, Adventurer's Vault 1 and 2, and Divine, Arcane and Martial Power, and even that is missing key pieces. Base 4th ed was totally playable, but a lot of important fixes have been introduced over time. Getting your paws on all the books leads to a legitimately better experience.
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Sburbopolis, Homestuck RPG: http://www.gamefaqs.com/boards/8-gamefaqs-contests/60981373