[eluser]Harold Villacorte[/eluser]
If a developer has never used Codeigniter before he/she would have to learn it just like any other framework. After doing a few projects with ZF2 I have to say that it is really not all that complicated, but it is definitely different from Codeigniter. The Codeigniter way is that everything extends the Super Object, that is what "$this" is all about. With ZF2 you do most of your work in a regular PHP way. You write classes, instantiate them, and pass the objects around.
If anyone is looking for another framework to learn my vote is for ZF2 with Doctrine 2. If you give yourself a little time to learn it you will be able to develop large complex applications in a relatively short amount of time. There are a few books out now on learning ZF2, so have at it.