I really think the Assassin needs something else added or changed to separated it from its Thief counterpart. Assassins specialize in killing. The Assassinate ability takes care of that. Specializing in killing requires being able to get close to your target yet the Assassin is worse than the thief which is already bad at level 1. I think removing more of the thief-like skills such as open locks, pick pockets would be appropriate. In return allow the Assassin to start with the same scores in Hide and Move Silently as the thief. Or even give them a slight boost. Doing this would really separate the Assassin into the more specialize class that he should be besides just being a gimped thief which is how the older versions were. So something like this at level 1:
Assassinate: I think this ability is fine the way it is.
Waylay: Fine the way it is.
Hide in Shadows: 15% (Slight boost)
Move Silently: 30% (Slight boost)
Listen: 30% (Same as thief as it should be)
Climb Walls: 80% (Same as thief as it should be)
Poison: 25% (This is fine though I'm not really sure what this ability actually does)
This would make the Assassin much better and more distinct from the Thief. You want to pick pockets, disarm traps, open locks roll a Thief. You want to slink in the shadows and assassinate enemies then roll an Assassin. Dimirag has a version of the Assassin that is much closer to what it should be. Just some thought after playing this class a lot. As it stands now, it seems lacking. Just my opinion of course.