I'll admit I haven't been logging my changes very carefully, but, off the top of my head:
TILE STUFF:
-All known "top-right-corner" and "top-left-corner" foreground tile issues = fixed
-Foreground/background issue at right edge of the grey steel platform and the pipe platform = fixed
-Foreground terrain that had masking issues because it was too narrow = fixed
-Background blue brick pattern = recolored slightly to look good on other people's monitors
-Various issues w/ background blue ventilator = fixed
-Various issues w/ background galaxy = fixed
-White pole which was missing the 'pole' property = fixed
-Inconsistent shading between 'on' and 'off' frames of platform switch = fixed
MISC:
-Dragon appears to get stuck less often or not at all
-All known level name bugs = fixed
-BAT cheat bug = fixed
LEVEL DESIGN CHANGES:
-FERN TOWN: Previously, there were two treats occupying the same space (one on the foreground layer and one on the info layer). This has been fixed.
-BEAN-WITH-BACON MEGAROCKET: Look down for a helpful surprise!
-TWO LINE TEMPLE: Long corridors have been shortened because they were boring; incorrect background tiles hiding behind switched platform = fixed
-SCULPTURE GARDEN: you can no longer find the foot without finding the 'secret switch' first. (Did anyone find the secret switch in the beta?)
-AIR QUALITY PLANT: there is now a barrier to prevent the monster from getting stuck in the tube
-TIME TEMPLE: Yellow key area is marked as 'optional'
-BADLUCK CAVE: Dropping platform near start no longer drops forever; spike-covered hill (which I felt was too close to the level start) has been shifted over slightly; switches in one of the blue areas are now marked in the order that you need to hit them in
-MOUNT MEURGLYS: Impossible-to-get treats have been removed; tile set has been simplified to solve a memory issue
-CANDY ISLAND: First switch puzzle has been simplified; chocolate bars are more clearly identifiable as solid foreground objects; yellow door bug fixed; green door area redesigned slightly; the Planet Cloudius insignia you sent me is hiding in here somewhere.

-WITCH DOCTOR'S HUT: Big platform area has been completely redesigned; one room has been removed to solve a memory issue; first area has been redesigned slightly, to make it more obvious that you're supposed to interact with the witch doctor
-SEWAGE PLANT (UPSTAIRS): Area directly above entrance is marked as 'optional'; the dead drop near the end will no longer take you into the path of a robot; a few of the toxic drops have been removed because they were too hard for the player to anticipate
-SEWAGE PLANT (DOWNSTAIRS): Hidden pipe entrances/exits are more clearly marked; there is now only one security drone (in the hidden area)
-RICK'S HIDEOUT: There is now a 'bunker' you can hide in while you wait for the platform at the very end; glitchy poles have been fixed; you can no longer bypass the traps in the green area