Pros:
-Nice opening and cutscenes
-The new mechanics are fine
-A few cute moments peppered throughout
-The artstyle of the cutscenes and character portraits are fine
Cons:
-Main gameplay is boring and tedious
-Soundtrack is very lacking compared to its predecessors
-Reused sprites from previous game (jarring when you consider the flatter backgrounds and radically different character portraits)
-Flatter and less colorful backgrounds that pop out much less than HGH
-Bosses are less interesting for numerous reasons (too much/too little health, boring mechanics, all have the same (bad) music)
Verdict: Definitely not worth $30, just play Pirate's Curse or Half Genie Hero, or literally any metroidvania. It will be a more pleasant experience. Watch the opening on YouTube tho.