I have recently been immersed in re-reading many of the Legion books and have been realizing that this is one of my favorite covers and was wondering why.
First it is a great cover image. Next it is of Mon-El and it is the last time he would be Mon-El as he was created, because he was been rewritten to become Valor and replace Superboy (who was written out of continuity) as the 20th century teen-age inspiration for the Legion. (Comic book continuity make Daytime TV soap continuity seem easy.)
Also the story itself was the last one before they started retro-conning the Legion to insane proportions which led to a total reboot.
Finally the story itself was a great one. Mon-El is fighting the Time Trapper and knows that if he destroys the Time Trapper he will wipe out everything that he knows, but if he doesn't wipe out the Time Trapper he risks allowing him to continue to be a puppet master and control the Legion. Mon-El does the right thing regardless of the personal cost.
This is a theme that I feel defines true heroism and I hope that on occasion I have lived my own life this way. Doing the right thing is what we have to do, regardless of the cost to ourselves.