Why it pays to ignore the rules sometimes

Last Friday we had a pretty satisfying gaming experience with my 4E D&D game, making it two pretty solid sessions in a row.  Both times I've begun to learn some lessons about what works and what doesn't.

First, the most recent session featured a Hannibal Lector-esque figure named Benalkazar (whose name was stolen shamelessly from some a family I know).  Benalkazar is a humanoid figure with a long robe, gloves, and mask who claims that he hasn't seen his face "in years."  The PC's don't know what he is.  Altered human? Demon?  Aberration?  Minor god?  He can do stuff magically that aren't in the rules, like perform rituals without materials.  He has a magic item also not in the rules.  And he basically snookered the PC's into releasing him from this prison, and then sent them an engraved thank-you note.  I half expected them to either side-track their current quest to go after him or at least file it away for a future quest, but instead the players were so impressed by his class that they are considering him for some sort of patron!

Magic items that aren't in the rules, spells that aren't in the rules, and NPC's that could be only-I-know-what.  All of these things seem to be making the game more interesting, which is good, because we are heading into our second year with this campaign.