After defeating all the currently available bosses, I can safely say the foundation's there, but it just really needs more polish. (Like the parry visual FX not always appearing, or the fact that after I defeated Dr. Chad, he got up and started attacking me while the victory screen was displayed) That, and while it's rather obvious flashing attacks are unblockable, it's never properly communicated to the player via text outside of experiencing it for themselves.
As for the bosses themselves, some of their attacks could use better telegraphing, or more consistent patterns. (Dr. Chad has a neigh-unreactable spinning swing, and sometimes he'll just spam unblockables, on top of that, sometimes he'll be left open after an unblockable, other times he'll follow up with yet another unblockable or more fast swings, which just makes the boss feel quite random, honestly.)
The other two bosses were fine once their patterns are memorized, imo.
As for other suggestions, there could probably be smaller, more easy enemies before throwing the player against a boss, as well as some way to heal mid-fight. (Like a mana bar that builds from parrying, that can be spent on either a big damage attack, or restoring heath)
Otherwise, neat game, just a lil' rough around the edges.