Demo's on PS3 sound like they're generally gimped - too short and too limited. The few PSP demos I tried were the same. Not the way to sell your product IMO.
Demos in general tend to be short and gimped, excepting those in PC land. (Since historically they've longer and more involved games in general, and have been sold off their multiplayer experiences for a lot longer.) This includes all the disc demos we've seen packaged with magazines in previous generations, too.
I don't have experience with the sum total of 360 demos (though playing with a friend in the Eternal Sonata demo makes me think it's just fine), but on the PS3 you have your short and crap (like The Simpsons game, which gives you one board, but tosses you in rather arbitrarily), your short and sweet (meaning "too short for how sweet it is," like Heavenly Sword), and your perfectly acceptable, like Folklore (especially since it now has two, the new one delivering an enhanced version of the Prologue of the release) and Stranglehold and Skate. I count the Ratchet and Clank demo among their number, as it delivered one level, but showed how varied even one level could be. It would certainly have been better delivered with an extra couple weapons (one involving the Sixaxis would be nice), and letting you actually go through the boss battle at the end of the level, instead of stopping right before it, but that doesn't make it a poor demo.
Most are simply... unimaginative and unstructured. I can play certain demos for a long time (say, Virtua Tennis) and get a very good feel for the general play of the game, and all they really do is limit your selectable characters and exclude a few modes. (Most games on console seem to limit any online multiplayer right now. That's one thing I wish they'd take a cue from PC's on. Why did I buy Battlefield 2 immediately...? Because I could PLAY an unrestricted Battlefield 2 board for as long as I wanted.) It's potentially long, but doesn't amount to a very enticing demo.
Even among the unimaginative, however, you can still get "enough." Most of the sports and racing titles give you a single game mode or a single board/track, and let you play as much as you want of it with a small subset of the playable characters/teams/cars/etc. But that can still get across a good feel for the game, as you know you'll be getting "more" from the release, but that it basically plays the same. (Those would especially benefit from demo multiplayer servers, however, so you can judge what online play will be like in as far as matchup and performance goes...)
Developers (though probably more the publishers) would certainly be better off spending more effort and delivering a tighter, longer, more interesting demo, but most haven't learned that yet. Publishers seem to think that a demo you push more resources into better demo will cost them on the front end AND counteract sales advantages by "giving people enough of the game to satisfy, so they won't bother buying the game." Frankly, I think it has a much larger effect of not only adding sales, but enticing the people who would likely pick up the game at some point regardless purchase it earlier at full price, instead of waiting. Case in point (or at least "anecdote"
), I have almost no interest in alternative sports titles at all, but I find myself going back to the Skate demo frequently because the delivered an in-depth tutorial and familiarization with the game, and gave plenty of time for me to play around by myself, unguided and uninterrupted, and a good-sized sandbox. It will probably be one of my next purchases in general, and really the first of that type of game I've purchased for any system at all.
My hope has gone up for demo quality, now that the systems can deliver them quickly, easily, and cheaply over network, though, and I've seen some improvements already. Hopefully the living and learning will continue on.