Khalin:

1) Sephiroth's appearance and personality can be considered cliche by now, but it was pretty original at the time. Remember that FFVII is a very old game.

2) Sephiroth was using Jenova's body to interact with you. So it's not true that he only appeared in flashbacks and at the end of the story. Because he was there, speaking and interacting with the characters all the time. The fact he was using Jenova's body to do it, is a mere detail.

3) Don't get me wrong, but I have the impression you read too much forum-debates about Sephiroth, where the haters state that "he only k1lled a flower g1rl!!1" or "he only destr0yed a v1llage!!1one!", and you forgot everything he actually did in the game.
Sephiroth did a lot of things. But there are many FFVII-haters who ignore it, and you shouldn't go by what they say.
Examples of his accomplishments that are ignored by the haters are: He killed everyone in the Shinra Building and Shinra Cargo Ship(while using Jenova's body), manipulated the party in giving the Black Materia to him, screwed Cloud's mind, was the responsible for all the chaos caused by the Weapons and Meteor, held back Holy(the only thing able to destroy Meteor), created a barrier around the Crater, absorbed tons of Lifestream, absorbed the Black Materia(you can see it attached to Safer Sephiroth's body), summoned Meteor(that destroyed Midgar), killed lots of people with Geostigma, etc.