Child of Eden

This is truly a beast of an achievement. The ratio does not lie. But you feel so damn proud after getting this! :D
Main point: you need to gold star all the archives on BOTH Normal and Hard. Hope is excluded from this (thank god!).

Gold star means 100% purification and more than 800,000 points (if playing with controller; for Kinect it's 500,000).
My suggestions are:
1) Be very comfortable with 100% purification, meaning know all the little "danger" spots for each level (such as killing someone either too late or too early). Check out the solutions for those 100% purification achievements, that was the help/boost I needed to make it work for me. Here are a few pointers on the "danger zones":

=== MTX
Area 3 (red squares): You must have 84% after killing the last wave of red squares. Killing the blue sphere to the end gives 16%.
Area 5 (4 red orbs): Make sure to kill the last blue snake in time, in order to get two big purple snakes.

=== EVO
Area 3: Those spinning purple enemies are annoying. You have to be very precise on timing with the last wave of those.

=== BTY
Area 1: After the two butterflies, the three flowers that release 8 enemies each. Make sure to octo lock and kill the enemies first and then kill the flowers. If you kill the flower too early you won't get all 8 enemies => will count as a miss on purification counter.
Area 3: The 8 enemies that come out in a spiral shape. There are three waves of those. Make sure to kill them in time, because if you don't they just get buried back into the tunnel. If you are too late you might still get the perfect octo-lock, but your "bullets" will be too late in reaching them before they burry again. Just make sure that your purification counter increased after killing them.

=== PSN
Area 2 (speedway with gates): After the 3rd gate, you get 6 and then 8 red dots. I personally used a euphoria here, because it was too annoying to try to kill them all in time before they fly away. Plus euphoria took care of the last gate too! ^.^
The rest of the level is hard, but everything is visible, so you just need to be fast enough (but don't forget about the beat!) ;)

=== JNY
Everything is very straight forward from the purification standpoint. Only the the "evo" themed area there are enemies that might get away from you if you are too slow, but otherwise you are just fighting bosses. Can't miss anyone here!

After being able to purify the socks our of each archive focus on keeping the beat and creating the cursor movement pattern from enemy to enemy.


2) Created mental "check points" at some Areas of the archive to make sure that you have enough points to make it to 800,000 in the end. The checkpoints below are very approximate, they are plus/minus 50,000 on either side. Sometimes you might do bad with normal enemies, but perfect with boss fights and still get 800K in the end, or vice versa, messing up bosses fights will put your efforts to waste.

=== MTX End of Area 2 (before red squares) ~ 130,000
=== MTX End of Area 4 (speedway) ~ 250,000
^^^ No Euphoria used (+100K)

=== EVO End of Area 2 (many little fishes + snakes) ~ 300,000
=== EVO End of Area 3 (with purple spinning enemies) ~ 400,000
^^^ No Euphoria used (+100K)

=== BTY End of Area 2 (before the tunnel) ~ 300,000
^^^ No Euphoria used (+100K)

=== PSN End of Area 5 (mirrors) ~ 600,000 (I was not planning on octo-locking the final boss because its too hard and used 1 Euphoria previously)
^^^ 1 Euphoria used in Area 2 (+50K)

=== JNY End of Area 4 (running men) ~ 350,000
^^^ 1 Euphoria used in Area 5 (+50K)


3) Lastly, practice, for the love of god, practice... and know that it's possible to get this cheevo, just might cost a bit of your sanity! ;)

Wishing everyone lots of patience!!! Please let me know if you have questions/concerns before down voting.

Since there is already an excellent guide above by ReDSHiFTD, there is not much else I can say in terms of specifics, so here's just some extra advice for this maddening challenge.

1. Take it slow and enjoy the ride. Don't jump in with the expectation to master it instantly. Doing so will overwhelm you and burn you out. The game is essentially a work of art, so it should be enjoyed as such during your first run through.

2. Learn the rhythm mechanic. This mechanic is described in more detail in the octa-lock guides. It is absolutely essential that you become proficient with this mechanic to increase your score. In addition to practicing the levels over and over again, you can look up the original Genki Rockets songs on Youtube to help yourself become more familiar with the beats.

3. Realize that the challenge is fair. Many eastern 'quarter eater' games like shmups and on-rails shooters are heavily weighted against the player to the point of being unfair. This is not one of those games. There is no ulterior motive to the difficulty here, only pure skill. Even the most difficult and chaotic sections of the game are designed in way that can be handled efficiently with the use of memorization, timing, and prioritization of targets.

4. Achieve an almost meditative state. As a good friend of mine once described it, meditation is the full effort and unity of the mind and body when engaged in a specific task. This concept fits well with the gameplay and is evident in the very soul of the work. Focus on your involvement with game and less on the achievements themselves. I know it's a fuzzy concept to describe, but I implore you to just try it and see if it improves your experience.

5. Let the music move you. This coincides with octa-locking and meditation, but it's important enough to warrant its own explanation. The music and lighting effects are almost always in sync with octa-lock moments and enemy attack patterns. Don't focus solely on octa-locking the targets, but instead focus on the beat. With proper attention, the music will act as a precursor to the obstacles and opportunities that would be quite unpredictable otherwise.

6. Train your eyes to notice the color purple. This may seem obvious, but just a second's delay in player response could mean doom in the harder levels. The color purple is almost exclusively used to show enemy projectiles, so learn to differentiate it from the mass of sensory overload. This also applies in reverse with orange representing a target.

7. Learn when to step back and cool off. Even with intense focus on the last step, failure is still inevitable. No matter how good you are, you will fail again, and again, and again. You'll get mad, you'll get sad, and you'll begin to lose proper judgement. This happened to all of us Eden veterans. Even if you've been playing the same level for hours straight, after a certain point it becomes better to attempt it another day. I'm not just saying this as a mental issue, there is evidence for the physiological side too. Our brains begin to reject and ignore repeat stimuli after overexposure, so I assure you that you're better off taking a break than continuing a marathon grind session.

8. Try out the different visual and auditory effects. To help counteract the above mentioned sensory fatigue, the visual filters and sound variations could provide some much appreciated variety. Some targets even become easier to see under certain conditions. Be aware though that this can also work in reverse and make some projectiles nearly invisible, so use with caution. This could also help with grinding the Lumi's Garden achievement too.

9. Consider trying out the game Rez HD. Child of Eden is essentially the spiritual successor to Rez, which was originally released on the Sega Dreamcast. Luckily the game received a HD remastering so it can be experienced via the XBLA for just $10. Choosing to play this game will provide extra experience with the gameplay type and reveal an interesting relationship between the two titles.

10. Don't underestimate yourself. This is my final and most important advice. I personally had no intention of completing this game when I started. It was so tough that I instantly became discouraged from even trying. That was my biggest mistake. With full effort and genuine motivation, you can achieve almost anything in life. All pros start out as utter noobs, but the transition can only begin if you are willing to try. Good luck and may the reflexes be with you.

Bonus tip: For quick reference, you can print out the various guides on this site, and then store them together by using the Kinect as a fancy paperweight.