The thing is that I really wanted to like Castles and Crusades.  I really wanted a cleaned up and functional AD&D.  I think part of the problem is that rpg designers don't really understand or respect D&D's wargame roots enough and tend to undermine its ability to do really big fights fast.  I'm not denying that it's more like the game people actually played a lot of the time but the strength of those roots emphasized.  Oh well, back to fiddling with Dark Passages III.

C&C was never my thing.

Bundle of Holding has a great deal on C&C right now, so I decided to take the plunge. I'll let you know what I think in a week or so, after I've done a read through.

I played C&C for awhile. It's super easy to house-rule and convert (older) D&D stuff. The siege IS wonky, but that can be house-ruled too. Adjusting it to 12/15, or using the 5e Advantage system for Primes instead.

The Saves system also needs house-ruling. The amount of typos can be kind of annoying. I do like the art, though it's kind of beef-cakey.

A bit off topic:
Someone mentioned Radiance, and my group switched to that from C&C. I found it well organized, with lots of options and a distinct steampunk feel. For a game with so many powers, the rules are too open-ended, I think. The optimizers in my groups were usually finding ways to abuse the rules.

Radiance is more complex (on the character side) than C&C, or most other retro-clones. It has a lot of moving parts. Your character can gain powers from race, class, theme, deity, magic items or electro-tech items, and more. Radiance is like a neat hybrid of 3e/4e with some AD&D sensibilities. My group abandoned it for 5e though. We've found 5e to be pretty darn balanced. It hits the sweet spot between rules-lite and complex-crunchy systems.

Castles & Crusades caught my eye in early 2007, before the wave of clones had crested.

As far as Siege goes, we've ported over how it's done in Amazing Adventures: 15 TN with a +5 bonus for Primes. Done. While the D&D "API" lends a lot of compatibility across the array of implementation, the Siege layer provides just a little extra to grab a hold of for winging it. TLG's price points and support certainly don't hurt either.

While I don't tend to run C&C, I really enjoy playing it. Actual play experience at the table is certainly my OSR.