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The original Rugby 08 contained fun but flawed gameplay (based off 06), OK graphics for its era, a licensed version of Saints & NZ, a fair selection of teams (half licensed) and laughable stats. Editing of the game is only possible thanks to mods.
Rugby Challenge contains fun but flawed gameplay (from scratch), OK graphics for its era, a licensed version of Saints & NZ, an excellent selection of teams (mostly licensed) and laughable stats. Editing of the game is available in-game.
What more is there to gauge from this comparison?