The Haunted Mansion may be getting old, but it's a classic. That the Haunted Mansion is still around is a tribute to the ingenuity of the original designers -- they worked wonders with huge elevators, black lights, fake mirrors and more. The Haunted House isn't actually scary (well, maybe for the really, really, young kids) but it is very, very cool. There's lots to see, the action is pretty much continuous, and some of the effects will leave you wondering, "how did they do that?" for weeks afterward.
The Hall of Presidents is some sort of presidentially-themed presentation that I didn't see.
The Liberty Belle Riverboat is a great big paddlewheel boat that runs along the "river" separating Liberty Square from Frontierland.