The left path is a bit weak. I like the visual of the second stage, but gameplay-wise it's pretty generic, as it's full of nothing but traps and generic needle. What I really liked was the right path. The visuals are amazing, and the jumps are more creative than in the left path (Left path's jumps aren't creative, actually), and the main part: There is a portal maze at the end of the second stage of this path, a really frustrating one. The boss isn't amazing, but it's nice, and forces you to move more than the one at the left path.
The penultimate stage loses a lot on the visuals. It's too simple, and doesn't really fit. The boss does a better job at it. Gameplay-wise, the situation is inverted. The stage is fairly fun, with screens of simple needle, followed by gigantic versions of the same screens, while the boss forces you to stand at a small platform dodging a lot of stuff while trying to kill him. The difficulty flag raises with this boss, but it's still plain tedious.
The last stage is very, very cool. It mixes the tilesets of all the previous stages into one, with a fitting background, in a big spiral screen. Nothing particularly hard, but then you reach the last boss. And here comes another difficulty leap.
The boss is a lot harder than it seems. His casting speed increases as his HP decreases, and after a while he's releasing simultaneous attacks (His huge amount of chasing attacks only makes things worse). He borrows attacks from all the previous bosses, and uses them in a more effective way, in a more effective screen. He has other tricks under his sleeve as well. Basically, he turns the 'dream' into a nightmare. But even so, it's still quite fun.
This game has plenty of ups and downs. If you don't mind the 'downs', I recommend it.