The Millie battle is highly unfair. She can go about 2x the speed of "Valkyrie", and she drives INTO you. She doesn't have an overheating arament, her bullets are huge, and she has about 10 times your amount of life. If that wasn't unfair, I'd give ths 4/5. Now, it's 3.
The boss is kind of stupid. Foirst you have to beat your way through 300 or so rubbish enemies, then once you've taken half his life he seems to loose less? Apart from the boss, 4/5.