Shakespeare introduces Helena to us as the character that nobody loves. She also has the most time to philosophize on the nature of love, maybe because she's not too busy actually being loved by anybody. Unlike Lysander, who speaks majestically of love (but in the specific contexts of history and poetry), Helena is prone to generalized statements. She dismisses love as a foolish child, but she isn't as delightful a character as As You Like It's Rosalind (who thinks the same thing). Why? Because love makes Helena a fool. It's hard to be sympathetic to her when she's so busy being self-pitying all the time.
Within the spectrum of lovers, Helena is the best representative of unrequited love. People who are in love might be fools (as witnessed by the other three youths), but people who are kept out of love are another brand of foolish.
In the play, even when Demetrius and Lysander both fall for Helena, she can't believe them. It seems Helena has spent so much time rationalizing why she isn't loved that, when the thing comes along (real or not), she can't embrace it and enjoy it for what it is. She becomes even more self-pitying when she believes that she has gone from a loner to a joke. Even at the end of the play, when Demetrius still loves her, Helena is skeptical.
Helena is Shakespeare's answer to what happens when things get too cerebral and self-indulgent around love—nobody loves a needy whiner. Helena needs to overcome her own insecurities. She should genuinely deal with them, instead of rationalizing them away by assuming she's just inferior to prettier women. Then, she might be able to relax and just enjoy love. There's a lesson for everybody here: Hermia needs to calm down, Lysander needs to toughen up, Demetrius needs to get off his high horse, and Helena needs to accept the confidence that comes with being loved.