Pylons
Block Swap
Major balance overhaul including finishing & overhauling Summoner and a bunch of reworks for other items
Automatic doors
Vanity graphics changes/improvements
Enemy banners being changed and made more useful
Boss health bars
More music tracks for existing bosses, biomes & events
New UI options in-game & Overhauled main menu UI
Tooltips have background for readability
Improved Guide & achievement system doing a better job at guiding new players
Numerous visual changes & improvements
Slightly more bearable early pre-boss gameplay in expert/master through food items dropping from trees
Overhauled desert biome
& More QoL additions & Fixes
1.4 has a HUGE amount of fixes, changes & QoL additions that added up and made the game refreshing and a lot more enjoyable to play. I didn't even dive into all the other additions and new features beyond fixes/QoL. Hell, the fact that you're more concerned about the
quantity of endgame bosses/content instead of the
quality of existing endgame content is pretty disagreeable. Lunar Pillars on Expert/Master and Moon Lord in general are tedious and unfair respectively, and pretty unfun either way.