Phew. I got home two days ago, but jet lag is a bitch. As is all the real life nonsense that I couldn't ignore after being away from home for three weeks.
Anyhoo...
Crunch. My favourite games over the years have all been crunch heavy. Hero, GURPS, Shadowrun, DnD3/Pathfinder1. They all have slightly different appeal to me.
Hero and GURPS have a great "build what you want" thing, be that thing a character or a campaign. They are also very easy to play.
DnD/Pathfinder are much more restricted than the others but there is a fun to be had in the mixing and matching of feats and the anticipation of getting to Level X, to get Feat Y, that will synergise with Class Ability Z to give all the whizz, Bang, POW!
Shadowrun has all that glorious gear porn. In addition, the sensibilities and implementation of the magic system really worked for me.
OH! I nearly forgot Ars Magica. I mean, it's the best magic system out there for that particular feel of a wizard in their tower studying arcane mysteries, building their knowledge and power over time, etc.
And honourable mentions to Rolemaster for the crit charts; and Twilight 2000 for yet more gear porn.
To specifically reply to the OP: I like crunch for both genre emulation and character differentiation. But I also like crunch for the gamist (is the word gamist? or am I using it wrong?) opportunities to manipulate the system and seeing what it can do in play.
I say genre emulation rather than "realism." I mean, I've been gaming so long I'm not sure what reality is anyway. But using crunch to generate realism will never get one more than a few key aspects that are important to whatever style of game is being played; which is to say one will wind up emulating a genre in any case.
DnD/Pathfinder aren't good at genre emulation. As people round here frequently say, DnD is a sub-genre all to itself; the system is pretty useless for emulating anything else. When it comes to being used in play I think the D20 system is a bit clunky. Well... very clunky. I've had 20 years of practice to get used to it but any time I introduce a new player to the system I get reminded of how unintuitive it is. Too many subsystems and unique ways of doing things. I consider the actual play of D20 to be an example of bad crunch. So I guess I like DnD crunch for character differentiation.
Shadowrun. (Only 1st ed. so all remarks are regarding that edition.) Again, it's own genre being the first (to my knowledge) to mash high fantasy and cyberpunk. That being said one could easily separate the magic and the cyberpunk to play a game of purely one genre or the other.
I think that in SR the crunch delivers for both genre emulation and character differentiation. So much of cyberpunk's genre appeal is the gear. And SR delivers on this. At the same time all that gear enables a lot of character differentiation. And then there's the magic and magical gear for yet more character differentiation and of course fantasy genre emulation.
I give SR good marks for consistently applying its dice conventions to all aspects of the game. This allows tech and magic to work together pretty well. (Aside: Those dice conventions weren't the best... Allowing people to manipulate both target numbers and the size of the dice pool made the thing a power gamer's paradise. Which I was cool with as player.

But power gaming makes it hard to GM a game.)
Hero and GURPS. I'll lump them together. Both very flexible crunch at the cost of great complexity. You can use the systems to create all the character differentiation you want. In both games the crunch is a) very consistently applied across the whole system; and b) mostly in character design. This makes them pretty easy to play once one has gotten the hang of the basic game conventions.
As for genre emulation they both have a good supply of genre/campaign source books. GURPS has the best library of these things out of any game system I know. Hero is a better tool for creating one's own genre stuff from scratch, this can be very time consuming of course. (I am currently doing the work for an L5R campaign using Hero. It is much work.) But at least you get exactly what you want.
So, yeah. There we go. A bunch of my thoughts on crunch with some specific examples.