quote: (post)

Originally posted by Sentry
Doesn't matter, blue or red supes, supes gets absorbed.

quote:

Kryptonite no longer seemed to affect Superman in his energy form. It was presumed this was because his DNA has changed completely (Superman #126).

It appeared that Magic (one of Superman's classic weaknesses) still held power over him in his new form. In AOS Annual #9, Superman found he was unable to absorb the punches or impacts he received while fighting a mythological being, and when he grabbed hold of a pendant hanging around the creature's neck he received a mighty shock. Superman himself pondered that the feeling "had magic written all over it!"
And again in Action Annual #9, (page 16) in a conversation with Lois, after dealing with a villain called Brother Serenity, Clark explained just how helpless he felt.

Also of note is the fact that Superman did not lose his powers when subjected to sunlight of a red sun (as seen in JLA/WildCATS). Therefore it was presumed that Earth's yellow sun was no longer the source of Superman's powers.

The following circumstances showed what Superman's weaknesses were in his energy form:

Excess Radiation Intake - Superman (and his containment suit) had a limit to how much radiation and energy he could absorb. Absorbing too much caused him pain and probably could have killed him (as seen in MOS #67).

Shock Pods acting like Tasers were seen to paralyse Superman in Action Comics #734, basically rendering him powerless.

An Energy Control being (an inhabitant of Kandor) was able to capture and contain Superman in Action Comics #734 using its ability to control all forms of energy it came in contact with.

Disrupter Cannon or similar technology caused Superman's energy form to disperse, which made it very hard for him to reform himself, and therefore he needed to revert to being Clark Kent to carry on. (as seen in Superman Annual #9)

Excessive use of powers - In AOS #549 Superman was seen to be "winded" after flying an elevator full of people out of his burning apartment building using his magnetic grip. He even admitted as much to Jimmy Olsen (pg 14).
Although this also could have been attributed to the fact that flight reduced the effect of Superman's magnetic grip (as seen in Action #738, pages 15 & 16). He had more control when he was standing on solid ground.