I've found that often the most surprising and enjoyable games are those you didn't know much about, wasn't a style you usually play, or just didn't think you would enjoy in the first place, but you tried it and suddenly found that you LOVE it.
Limbo for example, wasn't my cup of tea from first launch. Yet it hooked me and I found myself returning again and again to finish it.
It's often the overall experience, the atmosphere that seems to draw me in these days, and unfortunately finding a game that delivers on all levels seamlessly is rare. Most big gaming companies tend to "aim to win, but miss the point".