You can really see the artifacts of the default JPEG settings at ISO 1600, where detail in some areas is almost completely gone. If you're willing to trade off a slightly grainier look, though, the ISO 1600 shots may be quite usable when processed as raw.
Overall, the lens/camera system can deliver nicely sharp photos, but small details can start too look a little oversharpened. Look, for example, at the schmutz on the green parts of the daisy. However, you'll probably only notice it if you display the images at full size, and this type of sharpening will deliver photos that are good for printing.
(1/200 sec, f2.8, ISO 200, spot metering, AWB, 17mm lens)
The E-PL3 offers you the choice of how you want the low-light auto white balance to render the colors; corrected, as on the left, or preserving the warm tone conferred by indoor lights, as on the right.
(1/30 sec, f2.8, ISO 1600, spot metering, AWB, 17mm lens)