... the bad guys all had CS and that was what made us have to turn back and drop the trip. It was super effective but that was in long fights.
Pseudo hit the nail on the head. If you have a mage or cleric in the party CS ain't very useful.
The other thing (after "long fight"), is they "all had CS" (they probably outnumbered you as well). The apparent effectiveness of CS is getting a multiplier effect from everyone having it, versus the "true" effect of CS as experienced by a single rogue in a diverse party (see Pseudo above).
And if you don't have a mage or cleric in the party, then what do you think you are you doing?
You've got your mixed high level party with (say) a fighter/WM, a mage, a cleric and a rogue. How many rounds of melee combat does this party really have with each individual monster they're fighting before the fighter/WM downs it with his/her critical hits? Or, more likely still, the mage or cleric casts a spell to finish the beasty off? One? Two? Three at the outside?
it fails the save (even more rarely still)
If you can reliably land knockdown, CS provides very little additional utility in a crowd control sense. What CS is good for, is for long and grueling battles with hard-to-kill opponents, where the stacking effect of CS is allowed to accumulate. It's good, but not a top priority for any rogue build.
Immunity to ability drain negates CS? Does hiligrils amulet give you immunity to ability drain? I used it on one of my party members but he still got CS'd.
The NEP in the amulet does give these immunities, including to the effects of Crippling Strike, but of course it's as a spell with a temporary duration, and it can be dispelled.Negative energy protection - NWNWiki, the Neverwinter Nights Wiki - your guide to the game of NWN