I understand that Flash is by far the strongest summoner spell right now, and for a long time I thought it should be nerfed. However, after playing the game for quite some time and watching a lot of pro games, I think it should remain untouched. Flash promotes the type of aggressive gameplay that Riot seem to want. It makes viewing the game more exciting, as it creates windows of opportunity to score kills on enemy champions. Flash also allows allows the most creativity in its use. You can flash over a wall to surprise an enemy champion, or use it to juke back over a ridge to escape.
TLDR: Flash makes the game exciting! Keep it the way it is!