Your saves from v1.4 are NOT compatible. Your hats and settings should be fine, though.

[u]New Stuff:[/u]
-Paintings got reworked a bit. 25 new paintings were added. Some paintings only spawn in specific levels. It's much easier to add new paintings now.
-Added 3 new secret hats. Added a new way to unlock the monthly secret hats.
-Added a sound to jumppads and for when bosses get mad.
-Added a new secret mechanic to the game. (hint: try not murdering stuff this time) (also: you can disable this mechanic via console commands.)
[u][b]
Smaller Changes:[/b][/u]
-Fixed Pepper Boss not losing rage effects upon death, again.
-Certain scaling effects can now also change the hitboxes for actors. (Large/small objects should now have more accurate hitboxes.)
-Reduced performance by 90%.
-Nerfed bonus points given via enabling the Enemy HP Multiplier.
-You can no longer change the new difficulty modifiers via menus/console commands, without enabling cheats.
-Fixed rare cases where you could pick up specific items but not get any of it's associated score points due to differences in hitboxes.
-Changed the demo endscreen.
-Added some new obituaries.
-You can no longer carry trash bags across levels.
-Fixed the boss hp bar fade CVAR not being ON by default.
-The game now knows if you are playing on the demo version or not.