I just thought of an alternative payment route which might secure GOG some extra sales.
eMusic uses a subscription method for payment which involves paying a certain amount a month which gives you access to x amount of music. If you go under this amount, it doesn't roll over into the next month (which is perhaps a downside to using eMusic).
How many people would consider subscribing to GOG for (say, bimonthly access to) a number of games? I presume the incentive would be in dropping the price you effectively pay (i.e. pay as you go means 10 dollars a game, subscription means 7-8 dollars a game) for a game, with a possibility to pay as you go if you run out of 'game credits'. eMusic is very smart about its reaction to users going over their amount of songs per month, offering them instantly an upgrade to a wider (and more expensive) plan.
The parallels are there, eMusic sells DRM-free music, GOG.com sells DRM-free games. Perhaps GOG.com needs to expand its collection before launching a possible subscription plan (or it could offer trimester payment options, since the catalog for games is far smaller than the catalog for music anyway).
What do you guys think?

nah, it's perfect how it is. subscribing would suck because then you'd have people who have played all the games and not paid the full buy it price.

Unless the catalogue was approaching Steam or GameTap size (i.e. 100s of games), including much newer games, I don't think so. I happen to have an Audible (audiobooks) account that works on the credits system. However, audiobook prices vary widely (from under $5.00 to over $100, depending on length, author, publisher, etc.), so for audiobooks the credit system means that if you tend to want items that are over $20, the credit system represents substantial savings per audiobook. Whereas GOG only has two price levels, so it's hard to see how they could offer enough discount to make it worthwhile for their customers and still make a decent profit.

Music and Games are different animals. That kind of "rental" system would suppose some way of control, and for me control = drm.
I trully love GOG because I can download and own full games without any crap of control or DRM telling you what can you do and what can't you do with your own games.

I would not like a subscription because I like to play the games I pay for whenever I want and not worry that my time is running out.

Wouldn't the subscription "force" me to get something every 2 months? What if I don't like any of the games that have come out in those 2 months?

I don't really like the idea of subscriptions.
When I buy any game on GOG, I have the right to download and play it without any type of DRM or worry about tricky license terms. A subscription based system would complicate an otherwise established and convenient system.

There are 55 games available through GOG.com.
With a subscription process like you outlined (If I understand properly) someone could literally play each game probably within a small amount of time (not to full completion, obviously) and get out without ever paying the full price it would cost for those 55 games.
To me, it makes more sense to keep the current lineup for where you buy the games.
And again, like other people said, the main allure of the site is to buy the game, a subscription type method would mean the games would have DRM that would allow you to play as long as your account was current.
We don't need no DRM.

i already subscribe to far too many places as is. ill stick with buying them outright from this place.

I don't use subscriptions, or have any intention to sign up for one.
And as others have mentioned, you need to get several hundred (or better yet, thousands) of titles to make it worthwhile.