Nothing happens when I add a torrent or upon torrent completion. Nothing is added to the log and notify-send doesn't pop a notification on my desktop (but it does when I manually test it as above).
Just checking, Did you restart deluge after enabling the execute plugin. I was having the same issue, nothing happening on torrent complete. Once I restarted deluge, it started working.
I just rebuilt a new VM with v2.0.3 and reused the logic from my previous version 1 script. It works manually but I'm not even seeing the variables getting passed to new the script.
[...] but I'm not even seeing the variables getting passed to new the script
Did you test this from a script, e.g echoing $1-3 into text file for verification? There was a commit fixing windows support after deluge 2.0.3 released, but I see you're using Linux from your profile - you could try that updated newest version of plugin, from deluge develop branch, if verifying that it doesn't output vars correctly, just in case(place in your deluge profile dir and restart deluged):
(When searching back in my posts to find that link, saw a user stating it fixed his issue on raspbian and deluge 2.0.3 btw, so seemingly not 100% only windows related)