There are TONS of threads about just this topic. If you do a search, you will be sure to find some!
In a nutshell.....
Disneyworld is huge. All in all, it is bigger than the city of San Francisco. It has the four main parks (Magic Kingdom, Animal Kingdom, MGM and Epcot). Then it has two waterparks, 2 mini golf courses, a few big golf courses, a few lakes, 20+ hotels, and Downtown Disney.
You cannot get from one park to another without using transportation. The closest parks are at least a 10 minute drive from one to the other.
The parades, shows and fireworks are the same, and different.
WDW-no Aladdin show, they have Beauty and the Beast
WDW-no Billy Hill and the Hillbillies
Both have Fantasmic.
WDW also has Illuminations.
Animal Kingdom has Mickeys Jungle Jamming Parade.
MGM has the Stars and Motor Cars parade.
Magic Kingdom and
Disneyland are very very similar. In layout, rides, atmosphere.
MGM and California Adventure are somewhat the same.
You will find many rides the same, but some different ones at both parks. They both have Splash, Space, BTMR, Pirates, IASWorld, PPan, Teacups, etc...
Hotel prices, vary, depends what you are looking for.
I was always scared to go to Disneyworld. But we went this summer, and it was great. Huge, but great. We are now planning our 3rd trip to Disneyland. But I am sure we will return to Florida, especially if they offer free dining again!
Disneyland is smaller, more magical.
Disneyworld is larger, more 'wow' factor. (bigger castle, etc..)
Here is my opinion right after we returned...
http://www.disboards.com/showthread.php?t=1224824
You will enjoy WDW too!