Find gun stats

In a breif awnser

New single player missions carrying on where we ended MW2

Two new online game modes

Kill confirmed - Pick up dog tags of killed enemies to be credited with the kill or freindlys to deny the kill

Team Defender - First person who dies drops a flag the team who holds it longest wins

Kill streaks redesigned and a new form added where every 2 kills you get a new perk and at 8 you get all perks unlocked (Hardline does affect this meaning 7 kills for all)

New Spec ops missions ( Can be done on and offline)

And survival mode ( Can be done on and offline) - players fighting endless waves of enemies with each wave getting more difficult

Along with this weapons now have a thing called Proficiency where you have to level your gun up by using it to unlock things such as reduced kick and impact

From the Call of Duty Elite page, on which you can sign up for free and get the following:

1. PERSONAL Call of Duty® CAREER PROFILE

   Track thousands of gameplay stats, personal bests, & trends across Call of Duty® Black Ops, MW3 & all future enabled Call of Duty® games.

   • Career Stats
   • Recent Match Summaries
   • Performance Tracking
   • Create Custom Leaderboards
   • Showcase Trophies & Winnings
   • Spec Ops Stats
   • Private Match Data
   • News Feed
   • Notifications / Activity
   • Facebook Friend Import

You can find videos and screenshots of the Call of Duty Elite service. For example, a screenshot from the beta provides the data you're looking for: