Pretty good film, but here's my idea for a better ending.
I think a much cooler ending would be to have the group actually lose Quentin, so that he is left behind in the Cube without any knowledge of how to get out. So, the rest of the group (that earned it) would be shown making their way outside, with the final scene showing a desperate Quentin having to jump into rooms without knowing if they are traps or not, finally being killed by a unique trap that we have not seen before.
This would also be interesting because the opening and final scenes would feature someone being killed in a trap room.