Tom Clancy's Splinter Cell Essentials takes players deep into the Splinter Cell saga. Experience all-new missions and objective exclusive to the PSP system, and discover the untold story of Sam Fisher through flashbacks to various missions from the entire Splinter Cell franchise, including Tom Clancy's Splinter Cell Double Agent.

While Ubisoft's official Splinter Cell website treats this as an official game in the series, the game is mostly not consistent with either version of Splinter Cell: Double Agent. The Double Agent levels were changed dramatically in the console and PC versions and the timeline was also changed. Note that levels in either version of Double Agent are not consistent with each other as well. Between the three games there are three separate versions of the "Double Agent" storyline. Splinter Cell: Conviction may determine whether Lambert lived or not, and which version of the story is definitive.
(Wikipedia)

Cheats

Bonus missions:
Hold Select and press L, R, L, R, L, R at the bonus mission screen. Repeat the code to unlock the next bonus mission. The bonus missions are "Paris-Nice", "Heroin Factory", and "Television Free Indonesia".

All bonus missions:
Go to splintercellessentials.com on your PSP's Internet connection, select "PSP User", and enter A27200203S as a code.

Gameplay Hints

Splinter Cell Chaos Theory reference:
On the mission after the graveyard, get to the part where you escape from your cell. You will hear two men talking about what seems to be a football player being traded to another league. This same conversation can be overheard in Splinter Cell Chaos Theory, during the first mission in single player mode.


Here's the game's official trailer below: