English pronunciation is extremely hard. There are virtually no rules, you have to memorize pronunciation of each word individually. It is neither simple nor logical.
While English pronunciation/inventory may be harder than say Spanish or Italian, I think it's pretty middle-of-the-road compared to other languages in terms of size of inventory/difficulty.
[1] http://ohll.ish-lyon.cnrs.fr/fulltext/pellegrino/Pellegrino_...
The PDF linked is a draft of the paper, freely available; it's been removed from Academia, so here's the JSTOR link of the final release:
EDIT: Visit England you cunts (wrt downvotes).