At 32 you'll get Spinning Strike, which is an execute like ability that does lots of damage but can only be used on creatures with 30% or lower health. Also if you kill something with the standard saber strike you'll see some different finishing animations.

I love my infiltration shadow!! (level 32). It starts off slow but once you get your main abilities ( I have most of the melee moves cept for clairvoyant strike) it really picks up. Don't use SS as an opener..use breach of telekinetic throw..then I'll use double strike once to proc circling shadows, by this time Infiltration Tactics usually has proced and qyz normally has aggro so pop SS another double strike and then project at 50% the cost. If you need to SS something because qyz is dead or not holding aggro use Low Slash to get behind em.