eMachines used to have a terrible reputation. They have gotten much better in recent years, but still are lacking slightly compared to other companies. However, eMachines was recently bought by Gateway, which has helped reliability somewhat already. Their new laptop lines are supposedly very good, and I've heard much better things about their desktop systems.
For my money, I'd much rater build a system, but I wouldn't be too worried about eMachines overall anymore.