NOT that hard of a game
The music was awesome, the gameplay was awesome, the ONLY nitpick I had about this game was that when your mouse goes to the edges of the screen, your character gets "stuck", but that's more a flash limitation than anything else.
Anyone saying this is "too hard", I think you've been spoiled by current generation games: most NES, Genesis and SNES games were much harder than this.
As for Phanto, he's pretty easy to get by if you take into account something: he can't travel in reverse. So, just simply hang out near the right edge of the game, once Phanto appears, immediately position yourself directly above or below him, and he can't hit you.
Then, just back off some so you can see where he'll appear again, and repeat.
As for the stages themselves, I died about three times on the first two worlds (not counting the boss stages), so people complaining about a "sharp difficulty curve at the start", again, see the above paragraph about how games are way too easy nowadays.