Since I've been playing the rogue quite extensively, I think I'll add a bunch of input in for that class.
1)Right now I can't really pick a favorite skill, as all of the rogue's damaging abilities seems so similar just with different critical rates, which have kind of blurred at my current level (55.)
2)Insidious Poison, the damage it deals is so very low(At rank 5 its 2.8 dps for 10 seconds which is 28 damage) and it only applies on hits with skills so using a faster weapon and use left click attacks aren't even a viable strategy.
Viper Venom, same as above really, its damage isn't too great.
Charged Strike, it's very useful early on, but the damage scaling is pretty awful and nothing else about the abilities scales besides the duration, making it a one point wonder.
Shuriken, seems slightly promising, it just lacks quite a bit especially with how you can no longer move while throwing it (like in Din's Curse.) The damage scaling isn't too great either. I think this ability should have a cooldown and do a bit more damage and maybe slow the target.
Gouge, with the introduction of Cripple, it seems pointless to really invest into this skill. The flat values really fall off hard when you consider defense and attack values of 2000. The minor distraction is nice setup for other skills, but it needs some else going for it.
Dodge, the amount of defense and dodge you get per rank (25) is just way too low for the point investment. It does virtually nothing at my current level.
Feint, its effects replace Gouge and vice versa. Other than that, its pretty nice except the fact critical hit values get so high and its pretty much just a Major Distraction.
Jab, this skill just seems a bit too weak. Its concept is nice but I feel with how much damage you do later you can't counteract the hate you generate.
Caltrops, feels like its lacking something. It would be nice on a ranged character, but on the rogue you really have to be in the fight and the movement reduction doesn't help much unless you have to run.
Disarm Trap and Lock Pick, these abilities have such a weird scaling that if you do not put in tons of levels, they become useless at higher levels. They need a less flat scale in order to remain relevant.
Concentration: The cooldown on all of these are waaay too long. Concentration: Speed doesn't appear to increase use time of abilities (unless I just don't notice it), so it ends up being fairly useless in comparison to how useful it is to increase your defense a large amount using Concentration: Blur. Concentration: Poison should speak for itself, as noted about the other poison abilities.
3)Sleight of Hand is it really, none of the other skills really pop up as useless, they are just different ways of playing the rogue.
4) Dual Wielding in the Assassin tree would be neat. Maybe some sort of way to have skills do extra damage due to dual-wielding (to simulate hitting with both weapons), and attacking with basic attacks alternate between each. Would be expensive talent point wise, starting at 10.
Sword Mastery in the Assassin tree to rival that of Dagger Mastery, probably more focused around deep wounds.
Maybe a parry passive to mirror the dodge passive? it seems very roguey to me and would be another defensive skill to throw in.
Some sort of acrobatic leap ability for the Thief tree that would let you tumble short distances. Would give you increased dodge for the duration of the tumble and maybe it would give increased escape notice.
If I think of anything else I'll add it in. Overall the Rogue feels like it is in an okayish state. I think one of the main issues is that it lacks AoE compared to the other melee classes, and perhaps that's something else that should be looked at. Death Blow and Charged Strike being the only sources, but they don't do all that much damage to really matter. It wouldn't feel right giving them a really good skill, but maybe something a little more.
In addition to that, as I stated earlier, the lack of variety of abilities that do damage is another thing. At lower level they are very different but they eventually just blur together way too much.