Convolution reverbs are a form of software engineering voodoo that allow a user to have the reverb of an actual specific, pre-modeled space for use in their recordings that didn't happen in that space. It's complicated in it's design but the long and short of it is that you can dial up something like Avatar Studios drum room and use it for the reverb on your overheads. Pretty cool in theory.
The Waves IR-L is the less control endowed version of their convolution reverb the IR. It opens like any plug-in reverb and Waves has a wide selection of well liked and well known acoustic spaces that have been captured for use. The plug-in screen is simple with control for the Reverb time, the dry/wet blend, the predelay time and the output volume. There is a graph displaying the "appearance" of the reverb. You can load various "spaces" to hear as the reverb for your project. I have a few favorites of my own.
What I like about the IR-L is it's straightforward simplicity and sound. There are so many different spaces on offer that you would never be at a loss for getting the right verb. And the controls as so basic that getting the sound you want is quick and easy and fits right in provided you dial it in right. I use it all of the time even forsaking my other reverbs because I love it's workflow. The sound never disappoints me also. I'm a fan of primarily using it on drum overheads and for guitar verb sends when I need to give a mix a sense of space and realism. At it's price of $125 it's an excellent deal. I do highly recommend it to anyone.