It has positive and negative effects that vary not just from country to country but also within a country.
Let's assume that you are a low skilled worker in a traditional manafacturing country. Globalization bears the risk that these jobs slip away overseas or your wage decreases because your employer strives to reduce costs. Particularly vulnerable are the relatively unskilled and under-educated people, because they often can't adjust fast enough to changes. Globalization comes with a stronger use of IT-technology. Using this technology requires a certain level of education and flexibility. If you don't have it, you might lose out.
And if we look at market forces the picture is also not always a positive one. Given free reign, market forces give the rich the power to add further to their wealth. Large companies invest in poor countries only because they can make greater profits from low wage levels or because they can get access to their natural resources.
Okay, gotta go for now. If I've some more time later, I'll think of some pro-globalization arguments