Comparative Literature is usually interdepartmental, so it depends on what school you attend. Generally, though,
1) You have to read and analyze at least one non-English literature in the original language, so you will either have to be proficient in the given language before college or take classes in it in college.
2) Any good programme will have a theory component (Foucalt, Derrida, etc.) , which is usually absent from English Literature requirements. Theory is one of those things that you either love or hate.
3) You will also likely have to take classes in a third or fourth literature, usually in translation, and will be allowed to include other art forms like film, stagecraft, art (history, typically), architecture towards your requirements. I believe some colleges allow cultural studies classes to be counted towards requirements too.
Basically, English Literature is to Comp Lit as English is to Indo-European Languages.
Yes, like in any major that has 'literature' in teh title, you will read and write a lot. Like any major, the amount of work depends on the prof and the programme. It's harder than an English or (insert culture) major because of the language requirements, but you equally compromise depth in your focal literatures. I'd say an important thing to consider is whether your school has a separate comp lit department and its size. That can make or break your course of study.
source: comp lit major, saving up for foodstamps