Simply put: Alias is a hype job.
It pretends to be a lot of things that it's not.
First of all, it pretend to be that intelligent, complicated spy thriller. Of course, to be "intelligent" requires something other than ridiculous situations and plot holes galore. I know, that's exactly what 24 does... but 24 picked up the hype where Alias left it and is no more intelligent than Alias.
J.J. Abrams is really good at hyping himself, and unfortunately in today's Hollywood environment where TV executives are only worried about appearing hip and edgy, that's all that's required. Actual quality in J.J. Abrams' writing? There is none.
Then there is Jennifer Garner. A decent but not stellar actress in other projects, she gives some of her worst performances in alias. Why? Because all she does is pout and mug for the camera. Understandable. After all J.J. Abrams thinks of Alias as a fashion show and knows the only thing that'll keep them tuning in is to show Jennifer in various states of undress and funky costumes.
Look no further than the main titles to see that's all Alias was about: a fashion show.