$25 for a good adventure is not unreasonable. $25 for a poor adventure is most definately unreasonable. So, the real question is: is the adventure any good.
As for WotC's recent adventure offerings:
"Suns of Gruumsh": I liked it.
"The Twilight Tomb": Likewise, I liked it, though not as much.
"Red Hand of Doom": Excellent. Unquestionably the best of the bunch, IMO.
"Scourge of the Howling Horde": Truly woeful. Perhaps the worst 3.5e product produced.
"Expedition to Castle Ravenloft": I don't own this one, but it seems to be highly regarded.
"Expedition to Undermountain": Again, I don't own this one, but it seems to be poorly regarded.
"Expedition to the Demonweb Pits": This could have been really good, but falls short of its promise, IMO. If the DM is willing to do a lot of work, there is the shell of a really great campaign here.
"Expedition to the Ruins of Greyhawk": Again, this promises greatness, but falls short, IMO. It gets carried a certain distance on pure nostalgia, but that alone is not enough.
"Barrow of the Forgotten King": Good. Better than "Sons of Gruumsh", not as good as "Red Hand of Doom".
"The Sinister Spire": Better.
"Fortress of the Yuan-ti": Another solid adventure. Some parts are fantastic, while others are merely good.
"Keep on the Shadowfell": I don't own this one. Opinions appear to be generally good, with some dissent.
Unfortunately, this doesn't really tell us much. WotC are capable of producing some excellent adventures (and with the likes of Bruce Cordell and Ari Marmell available to write them, how could there be any doubt of that?), but their record has been somewhat patchy. I recommend waiting for the reviews.