I've never seen two cats react the same way to catnip. Oliver and Rocky enjoy it, Oliver more so. My RB cat Miles got really mellow after eating catnip -- he even took a nap a few times. Lucky was a "mean drunk" and would get aggressive, Peaches got really loving and demanding of attention, and Taffy wasn't even remotely interested in catnip.
Probably it's like humans and alcohol -- a lot depends on what's going on before Popsie has catnip.
Oliver is either weird or just a giant picky pants! He only reacts to certain brands of catnip (I know some contain lots of stems, but I've tried several brands trying to stay away from those that are mostly stem)... so far I've found he only reacts to Smarty Kat (they make all those cat toys out of leopard print fleece - he has the refillable mouse and a few others), Cosmic Cat nip, and whatever the heck kind came with his boogie mat! Any other kind gets NO reaction out of him... and I think the Smarty Kat is his most favorite brand... my dad loves when he's "high" lol
None of mine care for dried cat-nip, so I'm going to try them with fresh. I just planted some seeds, they came with a sample leaf and they enjoyed that.
Though hyping up Oci's really isn't needed, they are plently crazy already
I really think the brand and or growth stage play a role. Jamie only reacts to dried organic catnip from Canada. We have several catnip plants in our yard, and he only seems to react to them at certain stages of growth. Half the other cats in the neighborhood will react to them at any time, so I guess we're the local cat drug pushers.