When expressing emphasis, nothing else but seems to be quite an effective phrase; but there are numerous other phrases that convey a similar meaning. One of these is "nothing more than," which is a phrase that suggests that what is being discussed is quite simple or straightforward. "Only," "merely," and "exclusively" can all be used to suggest that something is the only thing of importance. "Purely," "uniquely," and "solely" suggest that something is entirely of singular importance. "Just," "simply," and "nothing other than" are also effective synonyms for nothing else but, conveying the idea that nothing else matters except what is being discussed.