由SEGA的Atomiswave基板開發，並於2006年移植至PlayStation 2的《越南大戰 6》（Metal Slug 6），是系列誕生十週年的紀念性大作。本作在系統與世界觀上展現出強烈的整合野心，不僅讓經典敵對勢力全面回歸，更首度與怒系列進行跨界聯動，將角色特色與動作射擊玩法推向新的高度，也象徵《越南大戰》邁入影音表現全面升級的新時代。

故事背景承接《越南大戰 3》之後的世界局勢。原本潰敗的火星人殘黨試圖再次與摩登將軍結盟，然而就在局勢尚未穩定之際，一股來自宇宙深處、更具侵略性的全新種族「金星人（Invader）」突然降臨地球。這些異形不僅吞噬火星人，還企圖將地球變為牠們的殖民地。面對滅絕級威脅，過去的敵人被迫放下仇恨，摩登軍團與正規軍甚至與火星人殘部共同組成前所未見的三方聯軍。除了熟悉的馬可、塔馬、菲歐與艾里之外，來自《怒》的 拉爾夫（Ralf） 與 克拉克（Clark） 也正式參戰，使整體戰鬥規模與角色陣容達到系列高峰。

在操作與系統設計方面，帶來關鍵性的革新，首次導入明確的「角色差異化系統」。過去角色僅止於外觀不同，但本作中每位角色皆擁有專屬能力，使戰術選擇更加多元。例如馬可的手槍威力顯著提升、塔馬在駕駛載具時具備更高耐久度、菲歐可直接持有重型武器登場，而拉爾夫與克拉克則融入近戰格鬥特色，前者能承受更多傷害並施展強力拳擊，後者則可使用投技在近距離造成巨大破壞。這種角色技能化設計大幅提升重複遊玩的策略深度。

此外，新增「雙武器切換系統」，允許玩家同時攜帶兩種特殊武器並自由切換，解決以往撿取新武器會覆蓋舊裝備的困擾。同時導入的「能量槽（Rush Blast）」機制，透過快速擊殺敵人累積計量表，當能量滿載時可觸發高分掉落效果，使整體戰鬥節奏更具爆發力與節拍感，也讓高分挑戰更加刺激。

在市場評價方面，普遍被視為「集大成且進化的里程碑之作」。受惠於 Atomiswave 基板性能提升，本作在背景層次、角色動畫以及巨大 Boss 的細節呈現上遠超過 Neo Geo 時期，尤其最終關卡於金星人巢穴中的激戰場面，展現出強烈的視覺震撼力。拉爾夫與克拉克的跨界參戰，更成功將硬派格鬥元素融合進射擊玩法之中，為系列帶來耳目一新的體驗。

當然，也有部分老玩家對於畫面轉向帶有3D渲染感的背景風格抱持保留態度，認為少了早期純手繪像素的細膩韻味；同時某些關卡設計（如地下蟲洞）難度偏高，對新手而言具有挑戰性。然而整體而言，PS2 版本提供的流暢操作、豐富隱藏要素與完整內容，使其成為家用平台上不可或缺的收藏作品。

《越南大戰 6》成功在致敬經典與創新突破之間取得平衡，不僅鞏固系列的歷史地位，也為這個橫跨十年的經典品牌注入嶄新的生命力。

Developed on the Atomiswave arcade hardware by SEGA and later ported to the PlayStation 2 in 2006, Metal Slug 6 (Metal Slug 6) was released as a commemorative title for the series’ 10th anniversary. The game demonstrates an ambitious effort to unify its systems and narrative, bringing back classic enemy factions while also featuring a crossover with Ikari Warriors. By introducing stronger character differentiation and refined action mechanics, it marked a new era of enhanced audiovisual quality for the franchise.

The story takes place shortly after the events of Metal Slug 3. The remnants of the defeated Mars People attempt to rebuild their alliance with General Morden, but before stability can be restored, a far more brutal and greedy alien race known as the “Invaders” descends upon Earth. These creatures not only prey on the Mars People but also aim to turn Earth into their colony. Faced with an extinction-level threat, former enemies are forced into an unprecedented alliance: Morden’s army, the regular forces, and the surviving Mars People unite to fight back. Alongside returning protagonists Marco, Tarma, Fio, and Eri, two iconic characters from Ikari Warriors—Ralf and Clark—join the battle, elevating both the scale and diversity of the conflict.

In terms of gameplay, Metal Slug 6 introduces a major innovation with its character differentiation system. Unlike previous entries where characters differed only cosmetically, each now possesses unique abilities that significantly impact strategy. Marco’s handgun deals increased damage, Tarma gains enhanced durability when piloting vehicles, and Fio starts with a heavy weapon. Ralf and Clark bring close-combat mechanics into the mix, with Ralf capable of taking additional hits and delivering powerful punches, while Clark can execute devastating grapples that grant temporary invincibility. This system greatly enhances replayability and tactical depth.

Another key addition is the dual weapon switching system, allowing players to carry and switch between two special weapons at will, eliminating the frustration of losing valuable firepower when picking up new items. The game also introduces the Rush Blast gauge, which fills as players defeat enemies rapidly. Once fully charged, it triggers increased coin drops for higher scores, adding rhythm and intensity to the combat while rewarding aggressive playstyles.

Critically, Metal Slug 6 received largely positive feedback and is often regarded as a “culmination and evolution” of the series. Thanks to the capabilities of the Atomiswave hardware, the game features richer background layers, more detailed animations, and massive bosses that surpass the visual fidelity of the Neo Geo era. The final battle within the Invaders’ hive stands out for its spectacular presentation. The crossover inclusion of Ralf and Clark was especially praised, successfully blending the gritty combat style of Ikari Warriors into the run-and-gun formula.

However, some longtime fans expressed reservations about the shift toward partially 3D-rendered backgrounds, feeling it lacked the charm of fully hand-drawn pixel art. Additionally, certain stages—such as the underground worm tunnels—were criticized for their punishing difficulty. Despite these concerns, the PS2 version’s smooth controls, additional content, and overall polish made it a must-have for home console players.

Ultimately, Metal Slug 6 strikes a successful balance between honoring the series’ legacy and embracing innovation, revitalizing the franchise and reaffirming its status as one of the defining names in side-scrolling action games.