I started playing casual games about three and a half years ago with games like the Tradewinds series, match-three games, and card games. I then developed quite a liking for the hidden object and time management games.
My interest has waned lately, I think, because I'm not really interested in games for small children (or with art or subject matter that seems directed to small children).
But the games with higher production values - and I've seen this in combination with hidden object techniques in particular - have begun more and more to incorporate adventure game techniques that require multiple steps - find the key, open the box, take out what's inside, set it aside for later use, etc.
(I never know whether I'm supposed to click it, drag it, move it, or what! Ergo, I speculate, the need for so many more of the strategy guides and "walkthroughs."
The need for these things didn't strike me as consistent with BrownEyedTigre's definition of a casual game as "a game that you can pick up and do with little instruction" and that's what really spurred my question as to the difference between "casual games" and "adventure games" as separate genres.)
Examples of these ne hidden object+adventure type of game would, I think, be Natalie Brooks, Escape the Museum, and the two new Sherlock Holmes games.
Although the hidden object elements advertised sometimes cause me some confusion, I've found upon closer inspection that they're usually pretty clearly identified as adventure-type casual games if you look (and you certainly find that out as soon as the game play starts, although I did learn from Escape the Museum never to buy without trying).
And there certainly have been hidden object games that do NOT include the adventure techniques - Hidden Mysteries: Civil War, the Hidden Object Show, Mystery P.I. - The Vegas Heist, the Nightshift Code. So it's not that I haven't had a number of choices within the genres that I enjoy.
I just think my time and money spent has declined simply because the production values of the games seems to be a little less than I've come to expect (I was surprised and a bit disappointed, for example, in what I perceived to be a slight decline in the production value of Agatha Christie: Peril at End House). And, again, the content themes of many of the "75% of the good old jump right in and play them" games seem to be directed at small children.
There are still lots of games for me to look forward to, of course - Hidden Expedition: Amazon for example! - but for some reason I'm just not finding as many as I'd liked in the past, I'm buying fewer games, uninstalling more and not playing as much.