Like most dissociatives, it is unpleasant until it "clicks".

Once it clicks, it is just as pleasurable as Ketamine, Methoxetamine, and other related ACHs.

One major difference between DXM and K is that DXM is quite stimulating whereas K is rather subdued and relaxing. If you don't have dissociative experience besides Ketamine, I'm not surprised that trying DXM after K would lead to an unpleasant experience.