Danc is still addicted to Dice Wars.
Personally, I can't stand Dice Wars. The optimum strategy in any given situation is pretty clear, so it's just an exersize in rolling dice. I prefer games with a significant skill challenge to them, either in terms of puzzles to solve, clicks to finesse, or both.
But Danc likes it - and so do many other people.
This is the crux of casual games. A casual game doesn't have to be a fantastically balanced piece of joy. So long as it offers infinite replayability - infinite variation - it has the potential to be a good casual game. The environment needs to be complex enough and variable enough that each game feels new.
Nearly all casual games simply randomize the letters. Randomize which letters are placed where, which cakes people order, which upgrades appear where... and that's fine.
Here's the weird thing about it, though.
After you've played a casual game for maybe five hours, you're not playing a casual game any more. You want more options, more complexity, more variation.
Most casual games have some kind of progression, with the idea that you can get further and further as you improve. The later levels will be more difficult, or arranged in more complex patterns.
These things don't make the game take much longer, but they add deeper elements. They make a given game more complex. Having to give up on words like "this" and "doggy" in order to clear letters with words like "ichor" and "egret" gives the player a challenge and keeps them interested.
That's not the most important part.
Challenge can be important, but it's doubly important never to stump the player. No popular casual game simply grinds to a halt if you can't figure something out. They give you hints, or run you out of time and kill you, or let you lose points to bypass, or let you make a bad move.
What you're looking for isn't difficulty so much as complexity. I don't mean complexity as in two hundred specific rules, I mean complexity as in simple rules, usually spatial rules, which produce a complex environment. The most popular games use either simple spacial rules on a board, or simple combinatory rules in a queue. You can make a new challenge, a complex challenge, by simply changing the board or the queue. The player never gets "stuck", they just get defeated or left behind.
If you're smart, you'll allow for that, too:
"Casual" doesn't have to mean "restart". I see no reason a casual game can't feature a loose campaign. Short games which further your position on a global map or other nearby players or something. It's important that you can't be surprisingly defeated in this long-term campaign, but it could allow you to add huge amounts of controllable variation to the casual game.
I have some ideas... how about you?