Size wise it is small 9.7cm (L) x 2.1cm (D) and 48.2 grams in weight.  Aluminum in construction with a tough anodized coating, construction overall is very high quality.  It houses a single AA battery which is able to drive the Cree 7090 XR-E LED through the use of a digitally controlled current regulation circuit.  Its important to note that current regulation is what you want when driving LEDs not voltage regulation.  Whilst the 'digitally controlled' part sounds like buzzwords it translates into constant current regulation at different output levels.  This is better than Pulse Width Modulation (PWM) output regulation which on low quality units results in a distracting flicker for some users.  This regulation circuit provide the flashlight with different brightness levels (4 in total) and modes (2 flashing modes), catering for the different purposes.  At its maximum level this torch is brighter than a 4D cell incandescent MagLite and the lowest level allow it to be used for 20-30hrs depending on the type of AA battery (Alkaline, Lithium, NiMH). Please refer to the following link for a comparison of brightness levels:

http://www.flashlightreviews.com/features/chart_manu.htm

The L1D CE really changes the way one thinks about flashlights.  The combination of new white LED technology and a great current regulation circuit means a large 4D cell incandescent MagLite can be replaced with a tiny torch that you can take anywhere.  A flashlight is most useful when its with you.  Though there are other reasons to carry a 4D cell MagLites, so they still have their use.