The rest of the storyline is actually garnered from earning audiologs that you can listen and read in your dossier in the main menu. While this is not a game I would ever pay $40.00 for, the 6.24 (including DLC) that I paid is more than worth it. Hell, I bought Bastion for $15 and was done with it in 5 hours.
It's worth the price, especially catching the sale. Now if only we could get an update on the trainer.
Not my cup of tea personally, but each to their own.
By the way, if you're still seeing it somewhere for $40, I'd start looking somewhere new. =P