It's nice and probably uses way less system resources, but it definitely isn't as "polished" as the Flash version was. Not sure if that's a limitation of the HTML5/JS/CSS combo or if they just need to work on it more. It's mostly just little things, like missing visual fade transitions or a UI that doesn't look like it's been repeatedly bleached. But they add up to a noticeable difference, I think--the HTML5 app just isn't as vibrant.

That being said, I always thought their Flash app was amazingly slick and polished, so it's a tough act to follow I suppose.

EDIT: Plus if they are going to go this far with HTML5 it'd be awesome if they could cut the Flash cord entirely. Not sure if that's technically possible though.