Surefire lights are generally regarded as being one of the highest quality manufacturers out there. Others include HDS Systems/Ra lights, and, well that's about it...
Surefire lights don't really ever tend to be the brightest, or fanciest, or have the most modes/gizmos, but they do produce a rock-solid light that will withstand some serious abuse. And if they ever do fail, their Customer Service is very good (by phone, apparently they are kind of slow by e-mail), and they often ask no questions and send a replacement part (such as tailcaps) within a few days.
Surefire is also a good benchmark by which to gauge the output of other lights, as Surefire rates the lumens their light produces in "out the front" lumens. Most other manufacturers rate their lights at "emitter lumens" and therefore, due to losses in the reflector/optic assembly and window glass, you will usually lose ~25% (a good benchmark #, some are more, others less) of emitter lumens when measuring "out the front" lumens.
Surefire lights tend to be more expensive than other lights, especially when you compare subjective things like output, run-times, User interfaces, modes (different levels of output), etc. But, unlike other lights out there, they are made here in America, and relied upon by members of our armed forces, various governmental agencies, etc. Basically, there warranty is "you break it, we fix it, forever" (batteries and bulbs not included, however).
Surefire makes Excellent lights, but they are not for everyone. If you need maximum output, go somewhere else, if you need maximum run-time, go somewhere else, if you like lights that have tons of modes, and whiz-bang gadgets, go somewhere else... But if need a light that is going to light up, every time, pick up a Surefire.