Voltaire on 12 September 2009
The arm cannon effects are in Echoes, but not Prime.
Corruption has a few changed. A room in Skytown (you had to time your screw attack jumps to avoid a spinning cylindical wall) is different. The wall does spin anymore, instead a green barrier replaces it. Its odd.
Also, when you beat Corruption, the Final Mission screen now says the completed difficulty. Dont see why they couldnt include it in the first 2 games.
