Revisiting this mod for the first time in 4 years was a great time, though one thing I definitely took note of moreso than before was how unbalanced the difficulty progression could be with multiple massive spikes up and down throughout the game that made me keep switching my world between Expert and Master with additional mods, otherwise things would suddenly get overly boring or frustrating without warning. Master specifically felt really weird, as throughout most of the vanilla progression the higher stats felt perfect with the increased DPS of calamity weapons, but it ultimately ends up into the same spongy mess that the vanilla difficulty is with post-Moon Lord enemies. This imbalance extends to weapons as well, with hundreds available but only a select few being viable at all.
While most of the bosses were fantastic, some of them such as the Twins and Skeletron were noticeably undertuned with Calamity balancing and were complete pushovers even on Master Death. Additionally, a few of the lategame ones I felt really needed more visual clarity on their attacks, such as Polterghast's tiny projectiles everywhere that are the same color as everything else in the fight, or the Thanatos Exo Mech that completely blends in with the fight's darkened background. Even with these issues though, this is still a modded favorite of mine I'd highly recommend, though maybe not for people unwilling to raise or lower difficulty mid-playthrough.