I've played a lot of Caustic.
His Ultimate is very situational, but honestly, it's F'ING AMAZING.
I tend to stack Ultimate Accelerants too, so I can spam that Ulti.
I have killed quite a few people with Caustic's Ulti, either in a building, or behind a rock, or whenever.
And whoever said Caustic wasn't getting a buff to his Ulti, is wrong.
Because he is...
No more will you toss your Ulti and have to wait a whole second to start seeing damage numbers before deciding it's worth it to run in your gas & take down that target.
Now you will see the damage numbers INSTANTLY, when thrown, so it will definitely help in reacting quicker (because a lot of the time you only get 1-2 seconds to target someone who's slowed within the gas...now you will get just that little bit longer, and they will take just a little bit more damage too).
His main issue for me, and the reason as to why I've swapped to Bangalore until the new Patch releases, is due to his hitbox.
The dude is huge, and an easy target, even in his gas.
Fixing the hitbox alone, is enough for me to play him again, as I personally made the gas work for me & my team.