The gameplay mechanics are basically the same as in SC. You control your character from a 3rd person perspective, and you have sneak through the levels, avoiding, or incapacitating enemy guards. But in addition to this there is small RPG like feature in it. On the levels you find various items, such as plastic bottles, rags, or ether flasks etc, and you can combine these into useful gadgets. Since the main character is a reporter, and not a soldier or command who can take anyone down with one hit, these gadgets are almost necessary for you to progress on the levels. For example, you can combine the plastic bottle and the rags, making a silencer that last for a number of shots. Or rags+ether flask=ether soaked rags, which can be used for a silent stealthy takedown. Oh, I almost forgot - knocked out enemies don't stay KOed for ever - you need to drug them with Anaesthetics to make them sleep long, otherwise they'll get up, and become pissed off. One more gadget I must mention is the X-Ray camera, which can be used for exploration (you can see through walls with it, and see the skeletons of the guards), and while you cannot take photos with it, you can use it do disable cameras, ignite flammable objects, or even to knock out guards. Priceless.
The graphics are quite good, IMO, but even the official reviews described it as "decent". So no super shiny shaders everywhere stuff (there are shaders of course), but it looks good, and it works well with the gameplay. Unfortunately the character animations are not the best - they are well detailed, but not really human-like, or physically correct.
The audio part is quite well done. The voice acting is very good, and musical score is also remarkable.
The AI is a bit mediocre, especially compared to SC, though you won't last long against them on combat (or at least I didn't manage). But if you stay hidden, it's fine. It seems this game is more based on stealth than on action, which is not a bad thing IMO. (though there are a few levels towards the endgame where you have to run'n'gun, but it's not that much, and the rest of the game compensates for it)
The story is excellent IMO. It brings together a bit of conspiracy theory and a fictional exlpanation of the 86' Cherobyl disaster. Very good mixture. The characters are also very well made, and they're all quite beleivable.

So, all in all, it's a very good game if you're looking for some sneaking with good atmosphere and story.

Ubisoft had confirmed that Splinter Cell Essentials, the franchise's first foray on the PSP, would be a prequel--meaning it would be an all-new title, not just a tweaked port.

So what of Splinter Cell Essentials, as Sam's first adventure on PSP is tentatively titled? Well, "It's not a port or a remix," Ubisoft says. The single-player game features nine missions - seven of the level maps are new, while the other two are taken from the first Splinter Cell game and Chaos Theory. Ubisoft reckons the whole thing should keep you occupied for around 13 hours.