Lightroom 4 introduces a new process version, PV2012. The new process version has totally revamped tone controls; as you noticed, for example, Fill Light and Recovery are gone. Generally, the approach in PV2012 is to work through the controls from top to bottom, starting with Exposure. When setting Exposure, you should concentrate on getting the midtones right (in contrast to PV2010, where you would set Exposure to avoid highlight clipping). Then work your way down through the rest of the tone controls. All of the PV2012 tone controls make the target brighter when moved to the right, and darker when moved to the left. So, for example, moving Shadows to the right will brighten the shadows much like the old Fill Light control.

Lightroom 4 still supports the PV2010 process that was the default in Lightroom 3. If you previously edited an image in Lightroom 3, it will still be in the PV2010 process, and the old tone controls like Fill Light will be visible. You can update an old image to PV2012 by clicking the exclamation point in the lower right corner of the image; however, the conversion is not exact, and you probably shouldn't update images indiscriminately.

Similarly, you can still work with new images in PV2010 in Lightroom 4 if you want to. Just select the 2010 process in the Camera Calibration panel of the Develop module.

Here is a video tutorial from Adobe that demonstrates the image update process and the new tone controls in Lightroom 4.