Runtime is quite long (regulated 8.5 hours on NiMH), and it also has a new reflector designed for the XP-E and XP-G that gives it good throw. It's also got a head switch.
I used Eneloop AA's in my ML125 when I first got it (NiMH pack was charging), and it worked fine. Runtime is a little short, and I don't want to use an odd number of AA's, so I'm back to using the NiMH pack. It was much lighter with the AA's though.