CodeIgniter is a fundamentally PHP4 system that is, today, wedged into more modern PHP5.3 programming practices. Personally, I can't see a good reason to use CI today (and I say that as someone who has used it extensively in the past--my capstone project at school was based on it!). If you want something CI-esque, you're better off looking at Kohana...but Kohana seems to give short shrift to certain important aspects, e.g. security is something of an afterthought.
Symfony2, on the other hand, can be pretty safely termed a modern system: it's almost completely modular (and not in the "override some files, it's like magic!" method of Kohana or CI), expects modern programming practices (it doesn't treat you like an idiot; you can use PHP 5.3 stuff like anonymous functions and it's cool with it), and is blazingly, blazingly fast when configured properly.
I disagree with your view of CodeIgniter. It's one of the best documented frameworks out there; it's quick to learn; and it doesn't require a lot of typing/coding. It's best suited for smaller projects, I would say, but for those projects it rocks.
CodeIgniter's documentation is indeed very good. Much better than Symfony2's, at least. I'd agree with you on that.
CodeIgniter also has no conception of how to actually work in PHP5.3. Perhaps CodeIgniter will acquire that down the road, but right now it's a poor routing kernel surrounded by a lot of inconsistent and very ugly modules that are duplicated or improved upon in the other major frameworks in common use.
"Doesn't require a lot of coding" is nonsensical; I can build a Symfony2 application to do nontrivial task in less time, with better and more reliable code, than I can the equivalent in CodeIgniter. And I used CodeIgniter since around the time of the original release. There are not many cases where something is top-to-bottom dominant in its field, but aside from documentation, which is being improved upon incrementally, Symfony2 really does fit that bill.
Symfony2, on the other hand, can be pretty safely termed a modern system: it's almost completely modular (and not in the "override some files, it's like magic!" method of Kohana or CI), expects modern programming practices (it doesn't treat you like an idiot; you can use PHP 5.3 stuff like anonymous functions and it's cool with it), and is blazingly, blazingly fast when configured properly.