Ahhh...I wasn't the only one to think it was that short
But I can tell you that DS I & II are worth it. Boss fights are challenging, especially the final one. When it wants to, they'll give you some kind of death spell that wipes you out no matter how high your HP.
To top it off, at least Indy gives us some stuff even if not enough $ compared to DS, so you really need to manage your HP/MP. If you're still up for the challenge, go ahead and check it out. You can always just play the 1 hour teaser.