I'd agree that the last few eps of Kolchak do seem to be running a bit out of steam, but I like The Sentry, or at least parts of it. I find the whole bit where Carl is on his own down there, running from the creature, very creepy, of course it's all ruined by the Gorn, er I mean the Sentry, but it is genunely scary for a while.
Re Depp as Kolchak. Actually I can see it. He can play crumpled, and the fact Edgar Wright is involved gives me a bit of hope as well.