Well, this is a review in progress, since I suspect my attitude may change after I've seen more episodes. Watching Samurai Jack may be like listening to Captain Beefheart. You suddenly 'get it' the 15th time.
"Samurai Jack' comes on in the early hours of the morning here, usually when I'm doing something else and not paying attention. When I have sat back and watched part of an episode, I've generally thought "What is this rubbish?" So last night I made sure to watch an entire episode carefully (it was ep XX, FWIW)
After watching it, my reaction is, "It still looks like rubbish, but it's a bit weird, and worth giving a second chance."
I've read tons of glowing reviews on imdb talking about the amazing animation and fantastic drawings. Are we watching the show? The one I'm watching has the main character sailing across the screen like Captain America in one of those awful 1960's TV cartoons, and the best I could say of the backgrounds is that they're bland.
Update: Ok, I've now seen 6 or so episodes. I've come to appreciate the clever use of widescreen vs 3:4 for different shots, the comic book layout of the thing, the general style - however I still find the episodes light on in the plot department. A triumph of style over substance, basically. Some episodes are straight out funny, others are straight out serious. Generally speaking I prefer the funny ones, which are usually good. The serious ones range from good to completely unremarkable.
It's pretty good in the style/technique/innovation depts., and quite funny at times, but I don't lose any sleep if I miss an episode.