I'm a fan of the Fenix E01. I like using a standard battery that I can get hold of anywhere, and I like being able to use a rechargeable (Eneloop) rather than disposable batteries.
And I like that it Saved My A*s Big Time on an impromptu alpine night navigation exercise last week, after I overestimated my ability to "just quickly nip up the Wendelstein" the afternoon after the first big snowfall of the year. The first hour or so of the descent, after enjoying the sunset from 300 metres below the summit, went well without a light – with afterglow, a rising full moon and snow on the ground, you don't need a light anyway. Below the snowline and into the trees was a different ballgame, however, and the Fenix turned out the be perfect for it – it throws a good twenty metres of enough light to find a steep, faint path in dense forest, but not so bright as to completely mess up my night vision for when I got back onto easier ground.
Other points that occur to me: lack of hands-free operation is a drawback; on the other hand, the fairly stiff twist action to turn on means there's no danger at all of accidentally draining the battery in your pack.
For anybody who really wants to get into flashlight obsessiveness, here's an unending and incredibly detailed review thread on the E01 at candlepower forums. They really like it.
http://www.candlepowerforums.com/vb/showthread.php?t=196078
I can think of better ways to save a couple of grams, if I cared, than carrying a toy plastic light.