I was just curious if anyone has an idea about the how long it will take to get through the singleplayer campaign? Is there any reason to replay the singleplayer? Awards? Collectibles?
 
I'm really trying to convince myself to buy this game but I am just afraid that after I play through it once I won't have anything else to do with it.

Probably a rent, but it's just a guess.

Well, there are a total of 240 Riddler trophies hidden all over Arkham Island, and since you are able to keep playing after you beat the game, that'd be a good way to get more out of the game. Plus you'd probably find spots you never thought would be there maybe.  
 
Other than that, there are the challenge rooms, along with possible DLC.

Length, Replayability...,ribbed for her pleasure?

" Length, Replayability...,ribbed for her pleasure? "

It's kinda irksome that none of the reviews have mentioned length. I know IGN said it took them 5 hours to get through chapter 1-4 (and they were playing through the first two chapters for the second time, so total would be like 6-7 for the first time through). Anyone know how many chapters are in the game?

Well if there are 240 riddler trophies, I guess they can't just have like 50 of them in the same chapter so I'm guessing 14-16 hours? 
 
I'm probably really, really off though.

i read on sum website that the game is around 15-20 hrs and once u beat the game the intire island is open to explor freely