In my opinion, it's not THAT hard, it just has an amazingly high learning curve. The hardest levels in the game are missions 1-3 the first time you play them. Once you get a hang of the fighting style, it gets a ton easier.
Stick with it, and fight your way to mission 10 or so. Once you do, you'll be amazed you ever had a problem with mission 2 or 3. If you're having trouble with mission 3, go back and play 1-2 a few more times, and earn some red orbs for equipment, extra blue orbs, and other stuff. Also, you can save your game in the pause menu before facing the boss, and that way if you die and have to start over, you can still keep the orbs and items you earned getting there.
Lastly, NEVER go into a boss battle without a yellow orb (at least 1). If you see a yellow god of time statue next to a door, there is probably a boss soon...so buy a yellow orb, unless you really feel like playing the mission over. Spend your first life learning the pattern, and save your healing items for later tries.
Yes, it can be frustrating, but its one of the best gaming experiences I've had in years.
