I can also only recommend digikam.
I've switched to it years ago while migrating from Mac/iPhoto and I'm quit happy with it. It's easy to group, classify, comment and tag images, it supports easy geotagging and it's open in that it can store all these meta data in standard format in the image itself.
The last point is the most important for me, because this means I'm not locked in into using digikam.
And if I need to do something special with the meta-data outside of digikam I can also script my images outside of it and later make digikam read the changed meta data.