I played through Modern Warfare (the first one) and I thought it was okay, if not a bit short, but I didn't have much interest in the multiplayer. I've been under the impression that most of these games are just designed primarily to update the online maps and features, and that little effort goes into the single player experience. When you think about it, these games do have a really short development window compared to most games, so it's no wonder.
I'm also not the biggest fan of games like Ghost Recon, or Dead Island, and I take it recent entries into the series borrow from these concepts. It just doesn't appeal to me. Honestly, the old school COD games are more appealing, the games based on actual wars. I remember enjoying the game "Deadly Dozen" on the PC back in the day.
But COD in space, or with zombies really doesn't sell me on the series. It's still one of the biggest cash cows in gaming right now. I have the same criticism/skepticism for games like Assassin's Creed, or anything that mashes out entry after entry, year after year, including Japanese titles like Tales.