Like many other things in today's world, the pace of development for cordless drills has accelerated over the last few years.  For more information on the best of the best you can visit this site on cordless drills.  The main contributor to this accelerated development has been battery technology.

Nickel Metal Hydride and Nickel Cadmium technology has been getting steadily better.  And the recent development of Lithium Ion battery technology has made a very large leap forward for batteries.  Of course, batteries are essential parts of cordless drills.  The more power the battery can hold the more power the cordless drill has.  Besides storing lots of energy you also want a battery to be able to charge quickly, discharge quickly, run through several duty cycles before wearing out, and be able to hold its charge while sitting idle.  Luckily lithium ion batteries excel in all those aspects.

This means that you can drill more holes with your cordless drill and that it has more torque to drill through brick or concrete.  It also means the drill will last longer.

There have been some other improvements as well.  The best cordless drill needs to be made of durable and light materials.  It also needs precision manufacturing.  We've had these things for quite a while, but they've gotten better over the last several years too.  Another nice development in recent years has been the LED light.  It's an odd thing to make cordless drills better, but having a built-in light on your drill is quite handy.  And old lighting technology just wasn't a good fit for cordless drills.  Old bulbs used too much power, gave off too much heat and burned out too fast to work in cordless drills.

Makita is a good example of a company that has used the LED to good effect in cordless drills.  Their newer drills have an LED bulb built-in that lights up whenever you're using the drill.

If you need more power than the standard 18v drill you can check out the best 24v cordless drill recommendations.