It's weird because the rules and system of C&C is very non-AD&D ( the reason I didn't buy it) (I did get the numbered mini-books box set, signed because I thought it was going to be like AD&D) but the stats are compatible with OAD&D. We've used our OAD&D/Hackmaster mix to play Castle Zagyg out of the box and it worked great. Just do 20- AC for the AD&D AC and use Specila abilites like poison or whatever from your system. ( We use hackmaster) Take mobs from which ever MM (1sted/HM)fits better and voila, that's it. So, yes it is compatible. ( You could even use some of the mobs as is if they have eight sided hit dice and just calculate experience with the chart) Oh I forgot, ignore any references to Prime attributes.
All that being said, I don't know how people can say it doesn't play like BD&D. I've played OAD&D for years and C&C doesn't emulate that game play. It's much more like BD&D,which I use to DM for my son when he was to young for the "older" rules. I just like more rules and I know older people still like OD&D and BD&D, I just don't and prefer a meatier system like OAD&D/Hackmaster or 3.5. (I guess I'm just not into rules "lite")
If its true that 3.5 is going to get the old modules updated like "Spies of Lightelf" then I'll take that over new material, plus we're still getting Tegel Manor. so it's all good and I can still use the C&C stuff like World Emperor or the modules.( if its too much of a pain to convert I'll just use it in my Greyhawk/Yggs setting) So I think everyone is going to "win" here.
Blue