I think it was a bit early to turn her at the end of season 3. And I read that Paul Wesley thought it was a bad move on the writers' part, and that it will really screw up Stefan's character, making him choose between Matt and Elena.

maybe if it had happened later in a season further away

It was a little early, but it had to happen eventually.

I think it was about time honestly. In the books Elena became a vampire by the end of book two. So season 3 was not too early. and having this happen isn't going to ruin Stefan's character but he is going to have to deal with letting her die to save Matt. Her dying wasn't his fault but he could have saved her. So no one is going to be happy with him. it shows in the preview for season 4.

I'm not really sure about it. I always thought that I didn't want her to become a vampire, but I really loved the season 3 finale and at the moment I'm really excited about her becoming a vampire, so I guess I'll just wait and see how it will turn out. Maybe after season 4 or half-way through I will know whether I like the decision to turn her.

Yes. 3 seasons human and maybe 3 seasons vampire....

maybe not in that way but YES