We probably should’ve released this two and a half years ago, but better late than never. The biggest changes include much lower memory usage (Windows should no longer crash on load), fixes to game-breaking bugs on several levels, new and remastered sounds, refined weapon physics, and fixes to the sources of frequent complaints in a few specific levels. A detailed (although not exhaustive) change log is included in a readme bundled with the game.
If you experience any problems, let us know; there probably won’t be a 1.2.2 release, unless anyone finds anything absolutely game-breaking, but we’ll at least know to fix it in 1.3 (which will hopefully see release in 2022, but all release date estimates from me should be taken with a massive grain of salt unless I explicitly state otherwise). Also, note that many of the biggest additions and changes (i.e., the new story elements, monsters, music, landscapes, weapons, and final boss battle) are being held for 1.3: we deliberately limited 1.2.1’s feature scope to ensure it would actually be released this year.