Firstly, and most importantly, there will be five new stages introduced. Five brand new stages, with five new backgrounds and even five new songs by the game's music man Baiyon. Not bad for a price of $5.99.
Next, a new feature introduced for Encore (hit three seeds in a row and all the bad guys EXPLODE) will be retroactively patched into the original game, which should make it a bit easier on you.
Finally, one level will introduce a "zero-G item", which when collected will let you float around to your heart's content, with no need to worry about silly little things like gravity.
Oh, and as for the "Big Secret(tm)" teased earlier in the month? They're still keeping mum on it, but did reveal that, if you get through the game and collect all 25 new spectra included, it "will enable you to play the entire game again in a completely different way".
With guns, perhaps?
PixelJunk Eden Encore Details [PlayStation]