Silver Fox wrote about left-handed friendliness, and I can't over-emphasize the importance of the ability to move a knife to either hand or either side of the body.
I get a little disappointed sometimes when someone makes a knife that actually favors the right hand and makes some minor concession to the left hand (such as a movable clip), and then they call it ambidextrous.
Spyderco makes some truly ambidextrous knives and that first attracted me to Spyderco.
Yes, we lefties represent only one seventh of the population.
It surprises me, though, that so many manufacturers of knives pass up on this easy way to increase their sales by 14%.
Silverfox also mentioned value and lockbacks.
The value for the money generally feels more right with Spyderco than other makers.
Some cheaper knives by other makers seem just that - cheap.
Some more expensive knives made by other makers seem overpriced for what the buyer gets.
Like I said, Spyderco seems just right.
I have a thing for lockbacks.
When done right, as Spyderco does it, a lockback has every virtue and none of the vices.
With or without the Boye dent, a lockback feels secure in my hand and I trust it not to close unexpectedly; I distrust all other locks in that regard, including the touted axis lock.
It mildly saddens me that BM has chosen to make their lockbacks so inelegant, as if to sabotage the entire concept.
Put it all together - true ambidexterity, value, and an elegant lockback - and it adds up to integrity; not only the integrity of the knife but the integrity of the maker.