I found myself recently wanting to play something straightforward on my work laptop, which was largely devoid of games. The Windows image used by our IT department is remarkably stripped-down -- far as I could figure, they took even Spider Solitaire off of it. And I *like* Spider: I've been a fan of the game since long before it was trendy.
So I went and looked up my old favorite, which I've been playing on and off for umpteen years now: Spider Wizard. Not a sophisticated game by any means -- I don't think it's changed noticeably since the XP version, and it's a bit overpriced by current standards. But it is, as the name suggests, essentially a configurable engine for Spider-like games, which provides room for rather more fun than average. And it has one of my all-time favorite horrible time-wasters: Grounds for Divorce.
It's a well-named solitaire variant, and the single most addictive version I've ever found. It's almost exactly like Spider, except for two rules tweaks and a program consideration:
1. Open stacks stay open when you deal. (Not unique, but not universal -- many Spider variants deal to the open pile, or don't allow you to deal if there is an open pile.)
2. All cards, including the buried ones, are visible.
3. Games only count for your stats if you actually move a card.
The thing is, Spider is largely a game of luck: there are a *lot* of face-down cards, so you're guessing a lot. I don't know if anyone's really studied it, but my guess is that, with the statistically best play, the game is probably only winnable half the time, because of how easy it is to get screwed by a down card. Not so with Grounds for Divorce -- since you can see all the played cards, you can actually strategize pretty deeply. Moreover, you can (and should) make an informed decision about whether to even accept a given tableau: my rule of thumb is to fully figure out whether I can do something interesting with the initial deal, and simply decline the game (with no penalty) if I can't. The result is that I win GfD about 3/4 of the time, and I suspect I could do better, making it a much more interesting (if still somewhat mindless and relaxing) challenge. It strikes a very good balance: hard enough that I do have to pay attention to what I'm doing, but eminently winnable.
So consider this a slightly guarded recommendation. Like I said, Spider Wizard is a bit primitive and over-priced by current standards. But I do find Grounds for Divorce worth the money in terms of how much I play it, the entire rest of the thing entirely aside...