SNK Playmore於2003年在NEO GEO平台推出，隨後移植至PlayStation 2的《越南大戰 5》（Metal Slug 5），是系列中風格最詭譎、神秘感最濃的一作。在經歷第四代素材重複與設計爭議後，本作開發團隊重新尋回系列早期的原創精神，大膽捨棄以往「摩登將軍」與「火星人」的元素，引入充滿異教崇拜與南美原始風情的全新敵對勢力，為硬派射擊遊戲注入神祕主義的冷冽氣息。

故事背景描繪一場與以往完全不同的戰場：正規軍的次世代Metal Slug開發資料被神秘組織「托勒密軍（Ptolemaic Army）」竊取。馬可、塔馬、菲歐與艾里四位老戰友再度集結，追蹤敵軍深入南美叢林與古代遺跡。隨著調查深入，他們發現敵軍不僅配備現代武裝，還崇拜某種超自然力量。遺跡深處，巨大的石像守衛和手持鐮刀的「死神」幻影紛紛現身，暗示這場奪還行動背後潛藏著足以毀滅世界的邪教儀式。整個劇情在充滿重金屬感的廢墟與地下祭壇中展開，巧妙地融合戰爭與靈異神怪元素，使玩家沉浸於冷冽神秘的冒險氛圍。

在操作與系統方面，最大革新是引入滑行（Sliding）動作。透過搖桿斜下配合跳躍鍵即可讓角色在地面快速滑行。這項功能徹底改變傳統僅靠跳躍迴避子彈的玩法，能穿梭於低空彈幕縫隙中，使戰鬥節奏更加流暢且具現代感。

載具系統也展現高度創意，其中最具代表性的是「Slug Gunner」，這款重裝機甲可雙足行走並切換坦克型態，配備火神砲與近戰大刀，即使面對巨型敵方機械依然能保持壓倒性火力。此外，如機動性極高的「Spider Slug」等載具，也配合多變地形設計，使玩家在戰場上靈活穿梭。雖然取消了前作的勳章系統，本作更強調移動技巧與火力覆蓋，回歸動作遊戲最原始的闖關樂趣。

市場評價方面，本作被視為一部具有高度「遺珠之憾」的作品。正面評價極力讚賞其視覺風格的突破與神級配樂，音樂以重金屬與搖滾為主，戰鬥節奏感十足，被許多粉絲認為是全系列最熱血的配樂。美術上，全新的敵兵設計和神秘遺跡場景展現開發團隊的創新野心，PS2版的流暢度更讓玩家完整體驗滑行動作的爽快感。

然而，遊戲也被批評內容有所刪減。原計畫有更宏大的劇情與分支，甚至包含未使用的魔王與關卡（如傳說中的巨大石龜），但受限於當時公司的財務與開發進度，最終版本略顯短促，最終魔王「死神」的戰鬥也顯得倉促收尾。儘管如此，《越南大戰 5》憑藉獨特風格與優異操作，在系列老玩家心中仍佔有一席之地，被視為雖殘缺卻極具個性的異色傑作。

Released by SNK Playmore in 2003 on the NEO GEO and later ported to the PlayStation 2, Metal Slug 5 is widely regarded as the most enigmatic and mysterious entry in the series. Following the controversies over asset reuse in the fourth installment, the development team sought to recapture the original spirit of the early games. They boldly abandoned the familiar “General Morden” and “Mars People” elements, introducing a new enemy faction inspired by pagan rituals and South American primitive culture, infusing the hardcore run-and-gun gameplay with a cold, mystical atmosphere.

The story unfolds on a battlefield unlike any before. The next-generation Metal Slug development data has been stolen by a mysterious organization known as the Ptolemaic Army. Marco, Tarma, Fio, and Eri reunite to track the enemy deep into remote South American jungles and ancient ruins. As they dig deeper, they discover that the enemy wields not only advanced modern weaponry but also reveres a supernatural force. In the depths of the ruins, massive stone guardians and scythe-wielding “Grim Reaper” phantoms appear, signaling that behind this retrieval mission lies a cult ritual capable of destroying the world. The narrative unfolds amid heavy-metal-styled ruins and subterranean altars, masterfully blending war with supernatural horror to immerse players in a chillingly mystical adventure.

Gameplay innovations are most notable in the introduction of the sliding mechanic. By pressing down on the joystick and combining it with the jump button, players can slide quickly along the ground. This fundamentally changes the traditional jump-to-dodge-bullets dynamic, allowing players to navigate low-altitude bullet patterns and creating a faster, more fluid combat rhythm.

The vehicle system also demonstrates remarkable creativity. The most iconic is the Slug Gunner, a heavy mech capable of walking on two legs and transforming into tank mode. Equipped with a Vulcan cannon and melee sword, it maintains overwhelming firepower even against giant mechanical enemies. Other vehicles, such as the highly mobile Spider Slug, complement the game’s varied terrain, giving players freedom to maneuver strategically. Although the medal system from the previous game was removed, Metal Slug 5 emphasizes pure movement skills and firepower coverage, returning to the series’ core run-and-gun thrill.

Critical reception recognizes Metal Slug 5 as a “hidden gem with a sense of regret.” Positive reviews praised its breakthrough visual style and outstanding soundtrack, dominated by heavy metal and rock influences, creating some of the most adrenaline-pumping music in the series. Art design—including new enemy designs and mysterious ruins—demonstrates the team’s creative ambition, and the PS2 version’s smooth performance allows players to fully enjoy the sliding mechanics.

However, the game faced criticism for significant content cuts. Originally planned with a more expansive story, multiple branching paths, and unused bosses and levels (such as the legendary giant stone turtle), the final release was somewhat truncated due to the company’s financial constraints and development timeline, making the final boss battle against the “Grim Reaper” feel rushed. Despite these shortcomings, Metal Slug 5 retains a place of respect among series veterans for its unique style and polished gameplay, standing as a distinctive, if incomplete, masterpiece in the franchise.