It's a very overdone cliche of "the badass/cool guy who keeps emotions bottled in". Even Sanji shows signs of sorrow/shock/relief. Since Skypiea, Zoro only seems to have two different facial expressions.
When I say he's the anti-Franky, I mean he's the polar opposite.
"Cliche", perhaps. But I think the word "archetype" might be better suited for this. See, there are only so many archetypes out there in manga-land : the money-hungry babe, the sensitive bad-ass, the insensitive badass, the underdog with lots of ambition but little self-confidence, the idiot savant, the myserious woman with a mysterious past … every single one of them is a "cliche" of shonen manga. A few quick examples off the top of my head:
money-hungry babe: Kaoru (RuroKen), Dakki (Houshin Engi), Nami, etc
sensitive badass: Kenshin (RuroKen), Kou Hiko (Houshin Engi), Sanji, etc
insensitive badass: Saito (RuroKen), Bunshuu (Houshin Engi), Zoro, etc
underdog: Yahiko (RuroKen), Youzen (Houshin Engi), Usopp, etc
idiot savant: Chou (RuroKen), Taikoubou (Houshin Engi), Luffy, etc …
mysterious woman: Megumi (RuroKen), Jyoka (Houshin Engi), Robin, etc …
So, as you can see here, it's almost impossible to come up with a totally unique character -- a character without previous archetypal qualities ... But that's not always a bad thing. We read stories with the expectation that a certain number of cliches will occur (a perfect example of this is how upset people get when their favorite character doesn't get a fight -- because even though "one fight per person" is a cliche, it's a cliche that most of us want/expect in this manga). "Cliche" isn't always a negative term.
What an author can do to make his charcters less cliched, is to give them little eccentricities and traits and quirks and so on. In this way, they are still true to the "archetype", but not identical to each other -- for instance, Kenshin and Sanji would never be mistaken for each other, even though both seem derived from the same archetype, because they are from different eras, have different reactions to women, have different hair-styles, and so on.
Yikes, this is becoming as dry and technical as a graduate thesis paper!!
Ok, let me simplify it like this:
Zoro is a cliche/archetype... So what?
If people enjoy him for what he is, then there's no stigma in that.
:)