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Quantum Conundrum: Season Pass is on sale for $19.99 at GMG. Use the voucher code QUANT-UMCON-UNDRM (Valid until 1100 UTC 23rd June 2012) for an extra 25% off, which makes the game only$15.
It uses STeamworks, so Steam activation is required.
The Season pass version comes with the full game of Quantum Conundrum plus 2 upcoming DLC packs, when they go live.