Yes, there are rules of English spelling. Go read all about them at Mark Rosenfelder's wonderful article Hou tu pranownse Inglish. It's just that the rules are way more complicated than any reasonable person would want to see, and about 15% of the words are plain irregular, including a lot of the most common ones. For example, you'd never guess that one is pronounced like won from just looking at it; you'd expect it to have the same vowel as alone and lonely, which indeed are related words: alone comes from all one, believe it or not.
But of course the very cream of the croup is ough, which can be pronounced in at least nine different ways (and I won't swear that I didn't leave any out):
- bough (rhymes with now)
- dough (rhymes with go)
- enough (rhymes with cuff)
- cough (rhymes with off)
- bought (rhymes with taut)
- through (rhymes with sue)
- hough (rhymes with lock, probably unique, also spelled "hock")
- hiccough (rhymes with up, probably unique, also spelled "hiccup")
- thorough (schwa vowel or short o, depending on dialect)
Some of these may not be distinct in your variety of English.
French, on the other hand, has equally complicated rules, but very few exceptions. Learn the system in all its hairy detail, and you're equipped to pronounce almost every French word at sight, impressing the hell out of your dining companions at French restaurants (until you have to admit that you have no idea what ris-de-veau a la financiere really is).
Indeed, the only exception I know of is the word oignon, meaning "onion"; you'd think the initial syllable was pronounced "wa", but in fact that i is inexplicably silent. Go figure.