There's a big difference between the old iPhoto and the newer edition. I prefer the old version. It's Edit mode was far easier to initiate; the new program requires extra steps. Not a big thing for one or two shots, but if you are processing a large collection, it can get a bit irritating.
The new iPhoto also seems awkward and dumbed down. With the old program, it was as if you were working with both hands; the new iPhoto's like working it with one hand behind the back.
You can't adjust the size and volume of images with as much ease. The bottom window must be moved out of the way to access the bottom corners of the 'crop' function. The straightening feature is nice. There is a 'balance scale' at the bottom of the image and a light grid for lining up the verticals in a shot. But be sure you straighten the photo before you crop it. Otherwise, you must go backward to access it.And will revert to the older version of the window if you crop first, then decide to straighten or level the shot. So you must return to crop and do that function again. Level first, then crop.
It is more difficult to access the data on size. With the older program, that information was available when you cropped and saved the image. With the new program, it isn't as forthcoming.
What I DO like in the new iPhoto is the capability to alter the overall image without going to Photoshop or another program. It's built right in and has a pretty good range.
At least enough for private family photos. You can lighten the exposure, 'warm up or cool down' the color, change the tint. That's really nice when working with old slides that have gone a bit blue with age or shots that were taken with too much or not enough light. I've been able to rehabilitate some old slides that would have been lost.
As far as slides of your work are concerned, it is my understanding that publications like Ceramics Monthly, Pottery Illustrated, etc. and some show juries and publishing editors will reject a slide outright if they see it has been processed through Photoshop or any other editing program.
Some people have told me the marking can removed, but frankly, that's just too much trouble for me. Better to take a really good slide in the first place. And if that's beyond your reach, get a set of good pro slides done.