In recent years there has been a fascination with not only ranking the top 10 games of a given year, but comparing the entire years themselves (i.e. the "is this years great games as good as 1998?" discussion). 2015 is a different kind of great year but one worthy of recognition imo.
Maybe it doesn't have the clear cut instant Legend like a Super Mario 64, a Grand Theft Auto III or a Half Life 2 that feels like it will change games forever. But what it does have, in spades, is sheer quantity of all-star caliber games in a wide swath of genres perhaps a number heretofore never seen before.
What's almost easy to forget is how different that is compared to where we were a mere 12 months ago. 2012-2014 were years with some really great underappreciated titles, but were years that didn't feel very deep, especially as some genres just didn't really have any compelling offerings for fans. And even recent strong years like 2010-2011 seemingly didn’t have more than a a couple dozen or so serious contenders at most.
That is definitely not the case this year. For example seriously just look at this list @little_socrates compiled of the games submitted by Giant Bomb's guest contributors. There is well over 100 games on that list (and growing), of which ~30 I could potentially see a good argument for my own list and at least 50+ I want to play at some point and another 5 or so I don't see on there that could be. Even high watermark years of days gone by rarely ever hit seemingly half that number. I suspect the proliferation of indie games have made this kind of variety a reality. It's simply fantastic.
What a great for playing games it's been. There has been so many, it's almost been stressful to try to make sure you don't miss out.
I think what I'm going to do in a year or so, is make another longer updated version of this list, because I think it could easily change to the point I might turn over half this list or more. e.g. I'm 90% sure once I get to Rise of the Tomb Raider it will likely knock something off here once I get to play it on PC.