As I expected, the candy series is a tough cookie, while the money scene is easiest to handle at higher ISOs, for reasons which should already be clear. ISO 100 is beautiful for all subjects, but all sensitivities up to ISO 800 look good enough for practically any use. Even the candy shadows at that last setting remind me of grain in well-behaved film.
Above ISO 800 things are not so peachy. First, the black level goes up, but that's not really a problem: it can be lowered in postprocessing. Then, we have higher noise amplitude. At ISO 1600 I could easily live with it, if not for the non-uniformity which starts showing up. Again, this is not obvious in the other two subjects, but see the shadow gradient at the bottom piece of yellow candy: while it is still reasonably gradual at ISO 800, at the next setting it starts showing blotches. At ISO 3200 this is additionally accompanied by a generous sprinkle of high-amplitude spikes.
Note, however, that some spots which look like noise spikes in the candy picture are not actually noise, but small crystals of (I hope) sugar: you can see them at all other ISOs as well.
To put things into perspective, remember than the 1:1 samples show how the image would look on a huge print, probably (depending on your monitor DPI) 20×107 cm, which should be viewed from a 1.2 m (4 ft) distance or so. Try to get a presentable print of this size from a 35-mm film frame, and only then complain about noise.
The detail is holding well up to ISO 1600, and so are the colors. I wouldn't be afraid to use this sensor gain occasionally, not just in emergencies.
Now, at ISO 3200 things may depend on the subject: for some pictures this speed may be quite usable, for others less so. The main problem may be in large areas devoid of any detail — in those I could detect some noise artifacts (blotching, slight banding) already at ISO 200 — see my white lily sample elsewhere.
By the way, I couldn't see any noise banding in the images shown here — but, again, this does not rather show in busy subjects.
As compared to...
As compared to the E-510, this camera introduces some improvement: while retaining the same, impressive amount of detail, it visibly improves the noise characteristics at ISO 800 and above (I don't see much difference below that); now ISO 3200 is as usable as ISO 1600 was, or, maybe, even a bit better.
Now, a tougher task: comparing the E-620 against its bigger, but barely older brother, the E-30. While just having a look at the similar E-30 samples, a better comparison can be made by flipping between corresponding samples in a full-screen image browser, and that's what I just did.
Based on these three subjects, the results are quite surprising: at the same (nominal) sharpness and NF settings the E-30 seems to have a slight edge at ISO 100 and 200 (more detail, cleaner noise pattern, especially at ISO 200), but at ISOs of 800 and beyond I like the E-620 more: the noise amplitude may be (just) a tad higher, but there is less detail loss due to filtering. (A downside is some occasional color artifact, I can see faint reddish blotches in the buckle image. Well, you cannot have it all!)