1) People simply experience things differently.
Members tend to over-generalize the most common examples onto everyone (like Oliver Cowdery's burning and stupor), but we are taught that the gifts and fruits of the Spirit are various and diverse. Some experience a unique calm; others a flash of insight ("pure intelligence"); others a cessation of worry or doubt (a "settling of the issue" feeling); others a sudden burst of joy; others, like me, a sense of peace. Whatever the specific manifestation, the person generally recognizes that they feel differently about it - that they no longer feel racked or tormented or pained by it. The "suffering" has been removed. That's enough for me.
2) I also believe the intensity of the feeling of forgiveness generally is commensurate with the level or degree of unrighteousness inherent in the actual sin. ("Your joy will be as sweet as your anguish was bitter.")
3) Most of us, however, don't go from sinning in a vile manner to sudden and full repentance. Most of us change gradually from one stage to another (line-upon-line, precept upon precept), so our recognition of the change (repentance) and the subsequent forgiveness is not nearly as intense as someone like Alma - or Zeezrom. Think about it: How many times in the entire scriptural canon do we read of experiences similar to
I really would rather not descend to the point where such a conversion and intense forgiveness would be possible, since I don't want to risk not being able to change. God had a specific mission for