I'm cautiously optimistic about this news. I'm just a casual game. I suspect that the vault will contain games that are 8-10 months old or older and have negligible sales. I don't mind paying 30$ a year to play older games. What this will do is eat into the secondary used game market (Gamestop, EB Games, Future Shop, etc..) as it will be cheaper to rent these older games than to buy even one used game, putting money in EAs pockets instead of these types of stores.
This being EA however, I wouldn't be surprised to see something like online multiplayer being a paid for DLC or something crazy like that, but time will tell.
The fine print also states that they can drop games from the vault at any time, so you can be SOL if you're in the middle of completing a game and that game is pulled. And the fine print also makes it very clear that this is a rental service. Stop paying for your sub and you lose access to the games that you downloaded.