Hey Pankaj - let me first answer the first part of your question by linking to another question I answered yesterday about the differences between Spring Security and other frameworks - JAAS and Shiro: Spring Security vs other frameworks
Now, looking at your list of technologies there, we have a few more. LDAP for example isn't necessarily a competing framework, it's more of an underlying tech that is usually used in the security stack, and yes, Spring Security has solid native integration with LDAP.
And Acegi is the old name of Spring Security - they're the same framework (of course Spring Security has evolved a lot since the days of Acegi).
Finally, the most exciting features - that's definitely an interesting question
I can tell you what I'm most excited about - it's the stuff in the last few modules of the course (have a look at the breakdown on the course page).
Hope that helps. Cheers,