I have tried Irfanview a couple of times in the past, it is a very impressive bit of work for one guy to come up with. Something with it isn't quite right though, it just doesn'y "feel" right compared to ACDSee Classic. I can't remember my contrete complaints with what it did.

It does do a lot more than ACDSee Classic does though, but they weren't things I needed it to do.

It is definitely worth a look for someone unhappy with their current view though.