Update at level 34 on Poison/Dual Pistols:
-Thought about shelving the character, but I decided to wait until picking up venomous gas. Well, I got it yesterday and it is...underwhelming. The debuff values are great and promising in theory, but with a 15' radius the power requires that I get uncomfortably close to the action for the debuffs to take effect. I regularly got pounded by AoEs and stuns when I edged close to the action to apply it. Drawing aggro was a problem too if the mobs hadn't been taunted or otherwise engaged yet.
-If it weren't for the "spines" sound effect on venomous gas, I wouldn't know that it was being applied. There's no clear visual zone of delineation between "debuffed" and "not being debuffed anymore and about to kill you", unlike with powers such as hurricane, time's juncture, or choking cloud. I've found this to be a theme with the whole set actually. There's not a ton of visual feedback about who has been debuffed, which makes spreading the love efficiently a bit of guessing game on a full team.
-For solo-ing mez=death. The gas gets toggled off and since the debuffs don't linger the mobs start hitting again right away. I've started carrying a tray of breakfrees. Feel a bit like a blaster, but without the damage or snazzy protection toggle. The set would really benefit from some position tools to make the most of the debuffs and venomous gas' small radius.
-Still struggling to deal with alphas, especially as more and more mobs have mez. Council vampires, for example, ruin my day if they don't get held by the gas trap--which is unreliable, even with the lockdown proc. I could target my debuffs on mezzers to initiate, but even then that leaves other mobs un-debuffed to wreck my face (e.g., the Warwolf throwing concrete at me), and doesn't solve the de-toggling problem. I'll be picking up my ST hold when I respec, but if there are multiple mezzers or other hard hitting mobs it's still a crap shoot.
-On the bright side: the -dmg stacking from chemical ammo, weaken, and venomous gas is pretty great. A +3 Warwolf boss swiped me for ~65 damage, after knocking me for about 4 times that earlier in the fight.
My ambivalence is resolving into a big nope, which is unfortunate since I like the char concept and I love defenders. A different secondary that offers more control and safety would probably help the situation. Dark especially, with its self-heal, -acc, and TT would be a great pairing. I could also see the set improving with incarnates and a lot of investment for ranged defense, but that's time and influence I'd rather save for a power-set that feels good out of the box.