Cavalary: While grouping is a good thing, I'd say that having groups expanded by default should be the rule, not the exception. Shows what's available at a glance, whether it contains what you actually searched for or not.
Hmm, interesting perspective. I'm collapsing them because I figure that if people aren't interested in a game, they're also not interested in the grouped products, plus I want to show as many games as possible per screen and games with 20+ expansions would then cause far too much scrolling.
...but yeah, maybe a full collapse is the wrong pattern, and I should always show at least ~5 lines for grouped products, with a "more..." button only if there are more (for the Paradoxes of this world).
Thanks! I'll mull this over a bit, but it feels like something worth experimenting with the next time I touch the front-end, and quite probably the right direction.