Demo: Seeing more than just the gameplay

I don't know why more companies don't do demos.  They're useful for more than just previewing the gameplay (although they are quite good for that).  It can be quite difficult to look at a game's stills and decide if it will be fun or not.  There's too much competition for my dollar to just throw money away on the prettiest pictures -- especially since that's become a major gimmick for making a crappy game sell better.  Considering how many free-to-play games there are entering the market, I find it even harder to spend money on something I'm not sure I'm going to like.  In this way the demo is especially important, but not 100% essential.

The other HUGE issues with demos for me, though, is the system specs.  It can be frustrating to pick up a new game from the store, take it home, and find out that the hardware specs don't match up.  This is especially true considering how flexible the definition of "runs" is for a game.  The other major thing that a demo does, especially for PC titles, is let me check my hardware and see if the game actually works for me or not, and it let's me gauge for myself what qualifies as "runs".  It's still not perfect, but it's still a whole lot better than taking a shot in the dark and discovering that you need some obscure hardware you didn't know about.

The last small thing is getting a feel for the game.  If your game sells itself on it's charm and personality, and not on innovative gameplay (simple solid gameplay is fine), then a demo let's you show that off.  The Recettear demo did this well.  I also thought the Dragon Age II demo let me see everything I needed to for making my decision, without giving away too much gameplay.  I bought Recettear immediately, and Dragon Age II found it's way onto my "watch for a sale" list.

And for a Fail demo, I call out the Geist demo.  I played the demo that came with my Cube when I bought it, which was simply the first level.  The problem with that is that Geist is a game with a lot of innovative gameplay, but the innovation wasn't showcased in the demo!  For example...

THAT'S A BIG DEAL!  That's 100% the draw of the game, and by not showing off that gameplay, the game looked like a standard survival horror game (and not a particularly good one).  If that demo had been better done -- possibly by presenting the content immediately after the spoiler event, then I'd have developed a much different impression of the game.

Does anyone else use demos for some other reason?  What are you looking at when you download a demo?  Is there anything in games that you wish you'd seen in a demo that would have changed your mind?  Any demos you'd like to call out as especially good or bad?