This is interesting. Eclipse4Web looks similar in nature to MyEclipse IDE (similar pricing model, similar enchancements to Eclipse, etc). Looks like Eclipse4Web focuses more on the UI and more on web frameworks, while MyEclipse focuses on J2EE development.
Personally, I like MyEclipse. For $30 a year you get a great plugin for Eclipse that really helps with J2EE development (servlet/JSP debugging, XDoclet assistance for multiple servlet and EJB containers, etc).
Maybe I'll shell out a few bucks and give Eclipse4Web a try =)