I would say give him a little more time, not only is he new to the Daily Show, he's a little less seasoned in life than Stewart and Colbert. If Stewart picked him to be his successor it was surely for a reason.
As far as the nightly show, the opening bit is usually pretty good, but the desk/panel format doesn't work well for me.
Have been pleasantly surprised by Colbert on Late Show - he hasn't totally abandoned his Colbert Report style and is bringing intelligent (and/or politically relevant + totally unintelligent) guests and discussions to the general public. People will only be smarter because of it, rather than the mindless drivel Letterman spewed.
John Oliver is also kicking ass, not surprising after his stint in the Daily Show chair.