Pretty much every cat I have ever owned has always liked catnip; so much so that they go nuts whenever I give them a catnip-related toy to play with. Why do some cats love it so much? What's in that stuff?
Interestingly enough, feline response to catnip is genetic in origin and not all cats respond to it. For example, cats in Australia generally don't respond.
At any rate, the active compound in catnip is nepetalacton which acts as a mood elevator in many cats and can make them happy. However, cat response to this being variable means that some can become overly aggressive. Alternatives, with similar chemical compounds that can cause like reactions include honeysuckle and valerian.