Struts2 is really WebWork 2 renamed as Struts2. Consider for a moment the fact that Struts essentially leveraged its own brand name to adopt WebWork as its new base, and that should suggest to you that there was at least some who felt it was very compelling — one doesn’t always throw out their own code base to start anew when they issue a sequel.
That said, I’m not going to tell you that Struts2 is better/worse than Spring 3 MVC. Bottom line is that they are definitely comparable.
If you want more details on how they compare, I suggest you check out Matt Raible’s presentations in years past on this topic:
http://raibledesigns.com/rd/entry/my_comparing_jvm_web_frameworks
http://static.raibledesigns.com/repository/presentations/ComparingJavaWebFrameworks-ApacheConUS2007.pdf
including a spreadsheet that compares several of them on various degrees:
http://spreadsheets.google.com/pub?key=0AtkkDCT2WDMXdC1HOEtnUHpCejJMbUhGeGJWUmh5dVE&hl=en&output=html