Pros
If you complain a lot to the academic director, s/he might give you what you want to shut you up (smaller class sizes, a lab class where you have to do nothing) but if you're a normal person with empathy and integrity, that will be taken advantage of. Your sick, personal and vacation days are fine, unless you start comparing them to that of public school teachers, which makes them look pathetic.
Cons
I'll start out by saying that those giving this company 5 stars are definitely plants from corporate, desperate for naive teachers, because the company is not doing well, thanks to the Saudi government refusing to pay scholarships for students not interested in going to class. They used to depend on that. ELS is a toxic environment. Like other reviewers have said, you only get paid for time in the classroom, even if you spend 4 hours grading essays on a Saturday and an hour or more per weeknight making tests and grading papers. As a teacher, you have homework and it adds up. ELS says you're "salaried" but that salary changes if you teach less hours, and they have found some kind of loophole so as not to pay you for the extra hours worked outside school. There's no bank of tests or lesson plans developed by other teachers who have taught the same book so you have to make your own as you go, which is extremely stressful in 4-week sessions. There's absolutely no opportunity for career advancement, the administration is completely useless and is reluctant to punish students for bad behavior because it's for-profit, and there are monthly unpaid training sessions. If you have years of experience but no master's, you start off at one measly rate. If you have a master's with zero classroom experience, you get $8/hr more. Go teach English in Korea -- it's the same pay, but someone else pays for your apartment, so you really live the high life compared to ELS at a whopping $24,000 per year, and they don't take 20% taxes either.