Stephen King teachs, bad things: "Sometimes they can back!" ... even with two X after the name.
"Ehi, have you any ideas for scam some money from PSP owners?" -say one of them-
"Sure" -answer the second- "We can convert Metal Slug 7 from Nintendo DS without any improvement neither in gameplay neither in the engine, it will be a two hours work"
"Metal Slug 7?!?" -exclaim the first- "But it is a so sucking game! We'll not find no one inclined to buy it."
"Don't worry. It will be enough to change the name. We'll call it Metal Slug XX, so someone will buy it thinking it is a new game, and some will read the double X and will take it believing is a porn." -say the second-
"Mmm, I don't know" -the first one seems dubious- "We could at least refine a little the graphical look."
"Man, you are really a nuisance! Ok, I'll redrawn the backgrounds graphic… shoot, another half a hour of work… I must go at home to see Unbeatable Banzuke!"
This is much likely how they decided to convert Metal Slug 7 for PSP.
The original game was so ridiculous and shameful to gain at once the prize for one of the most useless game on the NDS, besides being the most horrible episode of the Metal Slug saga.
Proud of this terrible work, Playmore's CUT & PASTE gifted programmers launch the game even on PSP, but aware it will be impossible to sell again that trash they thought well to change the name of the game, giving it the exotic suffix "XX".
Well, don't be fooled… XX is THE SAME of Metal Slug 7, with his dated graphic and sound, his poor level design, his awful game design, his preposterous difficulty, etc etc…
Starting from the graphical look, respect the prequels there are not any new enemies and sprites. All, and I repeat ALL the graphical elements moving on the screen was taken from previous games. A couple of elements can seem new, but really are mere redrawing of already know sprites. Only the bosses are original, but though well drew they lack in inspiration either in mere look than in attack routines.
Fully imported even the sound with sound effects and music taken shamefully from the prequels.
Levels design is simply ridiculous with ideas worthy of a two years old child (the mega cannonball following you around the levels? Commodore 64 stuff!!!), and don't speaking about some game design choice really awkward (like the level where each time you jump a parachute pop out from your back making avoid enemies bullets even more hard).
And it is not enough, some genius at SNK must thought: "Ehi, this game really sucks, but if the players are too busy avoiding enemies maybe they will not notice!"
So the difficult level of this game was set on "Hell on Hearth!"
Really, after the first mission is barely impossible make two steps in the game without die since the poor avatar is put constantly in situations where exit alive is absolutely impossible (this explains the presence of infinite continue).
Metal slug 7 was no reason to exist: stupid, presumptuous, deficient in every his features.
Metal Slug XX being a porting with only some (minor) improvements in graphic, inherit all the bad points of the original and therefore don't deserved to be bought from anyone.
If you want some more information you can read my Metal Slug 7 review, 'cause the game is the same, but even so I can say only a thing:
DON'T BUY THIS TRASH!!!