Kids do love WCS. Mine's been down a long time (needs some board work) and my kids (12 and 16) miss it. I also really enjoy the game, and have beat it, but its just really creative and colorful and well integrated and fun. Good gameplay.

FT is my favorite on your list. I think it has one of the tightest, elegant rule sets in pinball. Its a game that fights you a little and has huge risk reward opportunities. Perfect theme integration too.

NGG just annoys me. I've played the game live and on video pinball and I just can't get over the sounds and music and callouts Everything I thought I'd hate about FT but love. And hate on NGG.

Flintstones is a supercool game. I've played it far less then the others but always enjoy it. Great looking game too. So I don't really know how shallow it is. A shallow game can still have great staying power in a collection (like FT and IM), but it can also be boring as hell. Depends on the rules.