Your typical dissociatives (NMDA-antagonists) like Ketamine, DXM, nitrous, and PCP (I've never taken PCP so can't comment directly from experience) are not going to give you an experience that mimics that of traditional psychedelics (5-ht2a agonists). These dissociative's hallucinatory effects (or "trippy" effects) are mediated through their blocking (antagonism) of the NMDA ligand-gated ion channels (they attach to specific sites in the NMDA ion channel and prevents the channel from opening [uncompetitive antagonism], stopping the flow of Ca+ ions preventing an action potential from taking place). This is completely different than the agonism of your traditional psychedelics like LSD or Mushrooms on the 5-ht2a g protien coupled receptors, which are theorized to be the site of the hallucinatory effects (they attach to these specific serotonin binding sites triggering a response within the cell, aka causing a cascade of process with in the cell). So with all that said, the effects of your traditional psychedelics that has become to define what the expectation of the tripping experience is (obviously individual drugs have their own specific mode of action), doesn't share similarities to dissociatives like DXM. Not that dissociatives aren't mind manifesting, the subjective experience of the individual experiences a different form "trippyness". I find dissocitives to strip away the complex emotions leaving you with the primal emotions (of course high doses, the less and less the emotions become recognizable), and creates overwhelming sense of depersonalization, often leading to intense OBE (out of body experiences) and the ambiguous term ego-death. Sorry, I can't really explain the true differences of the traditional psychedelic experience and a dissociative experience, as its always hard to put into words not only a subjective experience, but a experience that really can only described by taking it.
It seems like most dissociatives have a weight dependent tolerance, so 354mg of DXM to me ,a 5'11" 185lb male, is a low ++ (see shulgin's scale, or the DXM plateau scale), while for my, ~5'8-10" ~110 lb, friend get rocked both by the hallucinatory effects and the nausea at the same dosage potentially bringing a solid +++. It takes me at least 650mg of DXM to achieve a +++ and at this point +708 mg to get to a strong +++ (OBEs, dex-hole).
I've stopped really trying to achieve strong +++'s on DXM alone at this point due to what I feel is raise in my permanent dissociative tolerance. I rather not go above 708mg of DXM for the increase side effects of taking so much DXM (after effects that seem to last longer than say ketamine) and for my stomachs sake (i have one hell of a time keeping down two bottles of Robitussin).