I've used iMovie before; mostly to do little more than a very simple assemble edit when I was in a hurry and didn't have access to Final Cut. And I did make an iMovie Trailer a couple of days ago and found that a lot of fun. But this was the first time I edited anything more complicated than that. Again, I haven't been using iMovie's previous release, so I don't even know what's different about this one, but some things I liked (Note: I know Audio Editing is new and improved in this release, the other features already existed in some form):
It's very easy to adjust audio levels, adjust fade ins and outs, and even fade down a portion in the middle of a clip. Even adding a sound track is very easy.
One of the really nice things about iMovie are it's templates that add some special graphic transitions. If you're throwing something together and these fit the project (and hopefully your audience hasn't seen them before!) you get very polished results.
The Clip Trimmer editor is great; it shows the clip, the part of the clip on screen, and the part of the clip taken up by any transitions. You can click to drag the visible part left or right, or click the in and out points to adjust the length of the clip. It's simple and intuitive:
There's lots of other little bits and pieces that work quite nicely, within a limited sphere. If you're throwing something together quickly, it mostly works; though I can't figure out how to do L-cuts in the Precision Editor.
So that's the good, here's some of the bad:
It crashed a couple of times on me, and that was in only a couple of hours of use. Since it auto-saves, I didn't really end up losing anything. I did however, at one point lose a bunch of adjustments I had made to the custom transitions. I'm not sure when that happened, so I don't know if it's because of one of the crashes, or whether I accidentally "Undid" something that cleared those out.
Performance is mostly very good, but now and again an update or redraw can take a while and it makes the performance of the application feel uneven. The Project window can be rather erratic when selecting a long part of a clip, moving a sound clip, or adjusting some of the complex transitions. This is because the clips in the Project are presented in an iconic view rather than a timeline, and it has to juggle things about when adding or selecting things.
When you're doing complicated things, it takes time to learn even a "simple" interface
As programs become more complex, it does get harder to parachute in and just do something; for example I only just figured how to display a single days clips in the clip bin! And while it lets you mark clips as favorites or rejects, I'd like to have sub folders I could place things in to reorganize content. iMovie have a pseudo timeline view, but I'm not sure it's any easier to work with than the regular view.
But iMovie isn't intended for really long and complex projects: and as a simple editor it's pretty good!