While the summer may be lacking in games compared to the Fall or Winter, I think you're passing over some of the newer gems that release as well. While the summer is certainly a time to catch up on games missed, some of the more curious titles that may get passed over traditionally become a success, or at least have the fighting chance to be.
If Knights in the Nightmare released at any other time, I wouldn't have the time for it. Other games would be put on top of my queue to play, and I may have skipped it completely. Instead, I got it and was completely shocked of its quality. It takes some time to get into, and it is certainly difficult (though it does include an Easy mode), but it is so creative and unique with the tactical RPG genre that it is incredibly fun and addicting. It's also the first game I gave a rating that WASN'T "rental" in months [http://www.gamertagged.net/index.php/article/review_knights_in_the_nightmare/]. While they are few and far between, there are a few titles that look to stand out this summer that wouldn't otherwise get the opportunity.
Then again, overall your point still stands, as there is usually still time between these releases to give older, cheaper titles a try. I guess the greater point is the summer is just a chance to not only play the mediocre and even terrible, but also to play what would often get ignored during the holiday season.