Something you have to keep in mind is he's recently been thrown into the discussion with guys like Catton, Lindstrom, Iginla, and (recently) Sennecke as far as guys in the mix in the mid to low top 10. I think people were expecting him to demonstrate that he belongs in that group, but he didn't have a particularly convincing showing.
In that range you are hoping to bet on upside for a top line player, and I just haven't seen anything out of Helenius at any level to suggest he'd be worth taking a swing at in that range. He'd be a great pick for a bubble team looking to add a solid versatile 2nd liner though (Buffalo or NJ for example).
WTK and I (and many others since we're pretty overrepresented on the site) are coming from the Habs board where Goldenhands (who, to his credit, called the last couple top 5 picks for us) has been hyping him up as being in, or ahead of most in that group, and I think we were hoping to see something we hadn't seen in Liiga to show he belongs there.
He's obviously a very smart player and has good (not great) tools, but I just don't see anything suggesting Aho/Suzuki kind of upside.