In kde3, when you were viewing an image in konqueror, there were shortcuts you could set to view the previous or next image in the folder. I think they were set to page down / page up by default.

In kde4, I can't find this functionality anywhere. Can anyone give any tips on how to set that up?

you could use the information panel in Dolphin with the up & down keys to get the same functionality

I am also missing the forward/backward functions for viewing a series of images. Together with the full-screen feature and the functions for zooming and rotating (which are still there), konqueror was perfect for image browsing. Now I am forced to start an external image browser for viewing more than one or two images. This is complicated by an annoying konqueror bug: When I say "Open with gwenview" on a selection of images, konqueror will start one gwenview instance for each image. After a few seconds all you can do is pull the plug ...

dolphin is no alternative for me; it is only a simple file manager while konqueror is a power-user shell; you can (at least in principle) manage your files, look into documents of all kinds, surf the web, use web applications, browse images, watch movies, look up installed packages, and so on, all at the same time and in the same window. dolphin is a step back into times where the desktop was cluttered up with too many windows.

Gwenview cannot open multiple files at once, an individual instance is needed for each. Thus Konqueror/Dolphin's behaviour is valid and expected.

What about the forward/back in the konqueror image viewer? Should I submit this as a bug?

The Konqueror image viewing capability is provided by Gwenview, please file a feature request at bugs.kde.org