Er, no it's not. This brief (and snarky) blog post pretty much sums up my feelings.
I've already been pretty critical of Arc, but pretty much ignored it after that. I've taken another peek and, once again, I'm still terribly impressed. Paul Graham has made arc code smaller for those projects he wants to focus on. He does this with decent libraries (well, decent if you don't mind 'ASCII-only' and layout controlled via HTML tables).
Welcome to the Intarweb, circa 1999.
I probably wouldn't be this harsh, but Graham has spent so long talking about "superior" programming languages that he pretty much had to knock this out of the park or tone his rhetoric down.