In order to unlock the "Insane" difficulty you must first complete all seven chapters on Hard. Take special care and do as the achievement description says: do not change the difficulty setting until you get the achievement. If you try to change it, you will get a warning message in the game, so no excuses! This stipulation applies during your playthrough on hard to unlock insane as well. So, when you're ready to start your insane playthrough, make sure you select "create new game" set the difficulty and then leave it alone until the achievement unlocks. Some people have reported that they did not get the achievement because they used chapter select on the first mission instead of "create new game".
Tips on actually beating insane/hard:
When a battle starts going badly and you need to retreat, use the
move while you have your stasis disc equipped (select it with
) and you will be invulnerable as long as you keep sprinting (hold
). You'll want to be sprinting to re-fill your health and energy. Once I figured out this technique, it saved me a lot of grief on some of the tough sections.
Pay close attention to the weaknesses/strengths information when it appears for a new enemy. You will need to exploit these to effectively deal with them. Even if it costs you a death or two to memorize the information it will pay off over time. Also, try experimenting with different disc powers on the various types of enemies, some may work unexpectedly well, especially when used in conjunction with multiple powers.
Lastly, if you really feel the need, you can "grind" on level 6 until you unlock more abilities, which will make your character stronger. If you are going to grind levels, it is recoomended that you do it while playing through the first time. All your stats will carry over and there is no experience increase from playing on higher difficulties. Starting Insane at level 50 is easier than starting at level 35. Please note that the game grid enhancers won't help you during the campaign.