It's hard and intensive, but thousands complete it every year so the horror stories are going over the top. They're trying to take people from different backgrounds and have them ready to start an entry-level teaching job in a short time, so there's a lot to cover. On many post-degree teacher training courses, the subject will have been covered before, but here they have to deal with that too. Look at job adverts and see how many specify it- if it weren't do-able, the jobs wouldn't be filled.
I have read many horror stories- some will be genuine, but many are posted by shills trying to encourage people to go for the Mickey Mouse courses available, and others come from people who seem to resent the fact that they were expected to work hard on an intensive training course. Take these away and you'll find some genuine grievances- courses aren't perfect and there are bad tutors to be found.
A lot of the horror stories is the distorting chatter you get on the internet. I could name a number of companies that I know have people regularly posting disinformation about the CELTA on various sites on the web. You don't need to be Stephen Hawkins to pass- you do need to be committed and prepared to work hard, think and do things a certain way.
Good luck with the course.
- For Teachers