I prefer smaller bundles, but I'm getting to the point that there aren't a lot of games that Amazon carries that I still want. My library has grown to the point that I'm only buying games I'm desperately in love with or are priced at 75% off or more.
The stuff I desperately want is typically new, and I almost always buy it from GMG because they have the best pre-order prices by far. The only new game I've ever bought from Amazon was Battlefield 3 and you guys ran like, a 42 dollar pre-order promo on it or something.
I think Amazon DVG is pretty much the best at everything but new release pre-order incentives. There you guys are about average. You probably don't have the pricing freedom that GreenManGaming does, so my suggestion would be to work in your strengths to supplement your weaknesses.
Example: Tomb Raider is coming out this year. It's been $35 dollars or lower on GMG a lot. I realize you guys can't meet that price. But you could get it at $45 and offer older Tomb Raider games free at the time of pre-purchase to make up that $10 difference. If I feel like catching up on new releases that I haven't played the old entries of, that deal becomes very enticing, because I'll be able to do that while I wait to play the new one I've already bought without paying anything extra.