If you've been to Ikea recently, you'll probably have seen the Perspex display cube featuring a chair being submitted to constant abuse by a robotic pneumatic arm. It's not there to imply that several centuries from now, when Earth is visited by a race of alien metal beings, the only things left standing will be Swedish flat-pack furniture, but rather to tell customers that they can purchase an Ikea chair safe in the knowledge that it's been rigorously tested.
If Sony had similar plans to convey the message of how sturdy the PSP's face buttons are, it would probably construct a glass sphere and place a student inside it, along with a PSP and a copy of Metal Slug Anthology. Or two of everything, if it wanted to demonstrate the ad hoc play in action.
That's because all seven games (Metal Slug, Metal Slug 2, Metal Slug X, Metal Slug 3, Metal Slug 4, Metal Slug 5 and the previously arcade-only Metal Slug 6) included on this UMD feature relentless side-scrolling shooting, requiring you to press the Square button with the kind of frequency and rapidity that would have Honda's Asimo wondering how long its digit bearings would last.
But one of the advantages of being human is feeling. So despite the incredibly repetitive nature of the dynamic at the core of Metal Slug (which does involve other buttons, clearly – you get to jump and throw grenades, too, as well as using the D-pad or analogue nub to move your little soldier around the screen), it's not something you'll notice due to the considerable joy you'll be experiencing while fighting on and in land, in the air, on water and under it.
That's surprising, because as some of the harshest games around, you'd expect future archaeologists to scratch their heads as to why they keep finding smashed PSPs with a copy of Metal Slug Anthology in the UMD drive, the wall against which the handhelds were thrown having long turned to dust. The Metal Slug series is the embodiment of the old-skool 'one shot kills' mechanic, and even its most recent iteration – despite incorporating a more contemporary feel, not least due to the increased fluidity of the main character – demands the eye-hand coordination of a cyborg.
Metal Slug titles are far from infuriating partly because they've charmingly rendered environments full of beautifully animated character sprites, as laden with humour as they are with artillery, but also because the game mechanic is honed as sharply as the knife your tiny avatar carries for close combat encounters.
Obviously much of the fun is the feeling of empowerment that comes from mowing down the attacking hordes with whatever firearm you happen to have in your hands. The default pistol is barely a pea-shooter, but saving the many POWs you find dotted around levels rewards you with access to more powerful weaponry, such as a machine gun, rocket launcher, guided missiles, flamethrower, bouncing bombs, laser gun, and a delightfully satisfying shotgun, to name but a handful.
Those will certainly help, of course, but they by no means guarantee progress, such is the onslaught of enemies you'll face – which depending on the Slug you're playing can be anything from soldiers, zombies and aliens to giant crustaceans, carnivorous plants and a troupe of yeti, plus bullets, grenades and countless aeroplanes, helicopters, boats and imaginative armoured vehicles.
A better option in order to reach the ridiculously resilient and pleasantly varied end-of-level bosses is to jump into one of the various vehicles occasionally available to you. It's usually far better to rely on the firepower of, say, a fighter jet, tank or canon-wielding camel than whatever else you may be carrying.
Don't be under the illusion that applying the above tactic will prevent you from using up Continues in order to, erm, continue your Metal Slug experience – finishing any of the series' games on just your initial three lives is a feat far beyond the reach of mere mortals.
Then again, beating the final boss because you've gluttoned your way through the unlimited credits you're given devalues the experience. Though not as much as the horrendous loading breaks that affect several of these games. While all the Slugs suffer from framerate slowdown during some of the mid- and end-boss encounters, overall this is mostly insignificant and not as annoying as the micro-pauses afflicting many of the titles on occasion.
And they certainly aren't as infuriating as the substantial mid-level recess that occurs on half of the games every time your character enters a new play environment (such as riding the sidecar on an AI-controlled bike), forcing the PSP to crudely load up the appropriate section. (Though you might expect otherwise, Metal Slug 6 actually deals with these in the most efficient and eloquent manner, incidentally.)
If that sounds like it's enough to murder Metal Slug Anthology's finer achievements, fear not. The slowdown is a significant wound, certainly, but the advantage of having seven very similar games (if nothing else, a perfect example of the Japanese sequel mentality) is that you still get the full Metal Slug experience from the iterations that have escaped serious injury.
Besides, we're being picky because we're fans of the series, and also because we aim to test games rigorously. After all, if you were buying a chair, you'd expect nothing less. So why not a game?