Roxas doesn't tap open treasure chests, he bitches them open
He walks differently than Sora
He carries his keyblade differently than Sora (none of that resting it on the shoulders crap)
Even when confused, Roxas is still a little bitch
You know that awesome looking recovery move? Yeah, he does that differently than Sora as well
During the final Axel fight, Roxas pins him on the ground with Clear Light (I'm fairly certain that's what it's called)- HELLO THEY'RE ALWAYS PINNING EACH OTHER DOWN!
In that same fight, if you hit Square, Roxas doesn't guard. Instead, he does some kickass fighting move.
Roxas is different than Sora
On the subject of the last one...I think that while Roxas is Sora's Nobody, that doesn't mean that they have to be similar. Especially when you consider that Roxas retained none of Sora's memories and had about a year to make himself his own person. Which he did.
And that is why there should be a way for Nobodies to get their hearts back without having to merge with their Other.
*fangirls some more*