I have level 3 on it until I level to 67. It does significantly more damage. It doesn't show up like regular spell crits; it just rolls by like a regular dot instead ;-( However, I was questioning whether lvl 3 of it was worth getting, and I'm very, very glad I got it. I will definitely go for the 4th level after hitting 67.
the crits dont show up like regular spell dmg. crits ( ala "... critical blast (xxxx).") but just show up if you have your per tic dmg. filter on. so say your a druid and you have your epic dot on a mob, the dmg. would show like ..
so and so has taken 55 dmg. so and so has taken 55 dmg. so and so has taken 110 dmg. <-- this is how crits show up.
i know, i was kinda hoping for the crit spam msg. myself, but CA does work and at lvl 1 it works pretty decent (w/ 4 dots stacked i get a crit from one every few rounds), cant wait to see what 2+ has to offer.