This will vary from person to person very much and it stems from what are they looking for in a game. Some love the crunch (comparing values and looking up tables) or rules-heavy systems (having rules defined for everything they could do in a game) and expect the system to be build in a way that system mastery is required. Some don't and will never read the CRB and I don't think it should be frowned upon.

My players liked the level of customization Shadowrun offers, with all the grip modifications and types of bullets. But then the only ones that didn't keep asking "how my main thing works, again?" were the ones who focused on ranged combat.

I probably could be a player in SR or D&D but I've discovered that for being GM, Savage Worlds (two dice defined by your character sheet to throw, against TN 4 in most cases) is the most crunch I can work with.
And max two books with rules; lore books - the more the merrier.