《越南大戰X》（Metal Slug X）是SNK於1999年推出的經典橫向捲軸射擊遊戲，實際上是《越南大戰2》的強化版本。該作並非單純的移植，而是對《越南大戰2》進行多方面的優化與改進，包括畫面表現、關卡設計、敵人配置和遊戲平衡性等，帶來更為流暢且充滿挑戰性的射擊體驗。作為該系列中備受推崇的作品，至今仍被認為是該系列的經典代表作之一。

劇情設定基本沿襲《越南大戰2》的背景：由於系列經典反派摩登將軍（General Morden）的軍隊再次崛起，世界陷入新的動盪之中。摩登這次似乎得到外星勢力的幫助，並計劃通過與外星人合作來奪取全球的控制權。為粉碎這場威脅，「遊隼突擊隊」（Peregrine Falcon Strike Force）四名精英成員—馬可（Marco Rossi）、塔瑪（Tarma Roving）、艾莉（Eri Kasamoto）和菲奧（Fio Germi），穿越多個充滿敵人和危機的戰場，阻止摩登和外星人的陰謀。

雖然劇情簡單，仍然延續該系列特有的幽默風格。敵人的誇張動作、角色的搞笑表情以及關卡中隨處可見的彩蛋為緊張的射擊戰鬥增添輕鬆氣氛。同時，外星元素的引入讓故事更具科幻色彩，增加與以往戰場背景截然不同的趣味性。

操作模式與系列傳統玩法保持一致。使用槍械、手榴彈和各種強大的載具來對抗蜂擁而至的敵軍和外星勢力。操作簡單直觀，但敵人的密集攻勢與場景陷阱要求玩家具備良好的反應能力和策略判斷。在武器方面，加入更多強大的武器選項，例如「鐳射槍」和「火焰槍」，並對原有武器的效果進行優化，使其火力表現更為突出。新增的武器種類使得戰鬥變得更加多樣化，也提升整體的選擇自由度。此外，仍然可以救援被俘的平民（人質）來獲得額外的武器和補給，這經典機制繼續激勵玩家在戰鬥中探索各種隱藏路徑。

值得一提的是，本作對《越南大戰2》的性能問題進行徹底改進。例如，《越南大戰2》中存在的掉幀現象在《越南大戰X》中得到修復，畫面更加流暢，操作手感也更為舒適，提供更理想的射擊體驗。關卡設計在保留《越南大戰2》框架的基礎上進行大幅優化。總共有六個關卡，每個關卡都包含多樣化的場景和敵人配置，從沙漠到軍事基地，再到外星人母艦，場景切換自然且視覺效果豐富。相較於原版，本作對關卡中的敵人位置、道具分佈以及難度進行重新調整。例如，某些敵人的出現時間被重新設計，讓戰鬥節奏更加緊湊；關卡中隱藏的武器和補給點也更加合理。此外，導入新的夜晚場景和天氣效果（如沙塵暴），這些細節讓戰場更加真實，並增加戰鬥過程中的視覺變化。

BOSS戰作為《越南大戰》系列的亮點，研發團隊也進行改進與調整。每個BOSS都擁有極具挑戰性的攻擊模式，例如巨型戰車、多段形態變化的外星飛船，甚至是擁有強大火力的機甲。這些戰鬥需要在攻擊與閃避間做出精準的判斷，使每場BOSS戰既緊張又充滿成就感。在畫面表現上延續系列一貫的高水準。細膩的像素藝術風格充滿細節，角色動作流暢，敵人和場景背景的設計生動且充滿幽默感。爆炸特效和載具細節也經過強化，讓戰鬥過程更加華麗。音樂方面，採用大量重新編曲的背景音樂，為戰鬥增添更多緊張感和動感。每個關卡的音樂風格都與場景氣氛高度契合，特別是夜晚場景和最終決戰的音樂設計，更加烘托劇情的高潮。

當時在推出後獲得廣泛的好評。評論家和玩家一致認為，本作成功解決《越南大戰2》中存在的技術問題，並通過調整敵人配置和優化玩法細節，提供更加完善的冒險體驗。許多玩家認為，《越南大戰X》是該系列中難度最平衡且節奏最緊湊的作品，適合新手和資深玩家共同挑戰。然而，部分評論也指出，作為《越南大戰2》的強化版，在創新方面表現不足，主要依賴於原版的框架和素材。儘管如此，這並未影響遊戲的受歡迎程度，因為其優化和改進足以讓玩家忽略這缺點。

整體而言，《越南大戰X》是《越南大戰》系列的經典之作，在保留原有特色的同時，進一步提升可玩性與流暢度，成為許多玩家心目中無法替代的經典記憶。即便在多年後，該作依然是2D橫向捲軸射擊遊戲的模範之作，對系列及整個遊戲產業產生深遠的影響。

Metal Slug X, released by SNK in 1999, is a classic side-scrolling shooter and an enhanced version of Metal Slug 2. Rather than being a mere port, the game features comprehensive optimizations and improvements over its predecessor, including visual performance, level design, enemy placements, and gameplay balance. These refinements deliver a smoother and more challenging shooting experience, solidifying its reputation as one of the most iconic entries in the series.

Story and Setting

The narrative closely follows the backdrop of Metal Slug 2: the infamous antagonist General Morden’s army has risen again, plunging the world into turmoil. This time, Morden appears to have allied with extraterrestrial forces, aiming to seize global control. To thwart this looming threat, the elite members of the Peregrine Falcon Strike Force—Marco Rossi, Tarma Roving, Eri Kasamoto, and Fio Germi—embark on missions across battlefields teeming with enemies and dangers to stop Morden and his alien allies.

Despite its straightforward storyline, the game retains the series’ signature humor. Exaggerated enemy animations, comical character expressions, and numerous Easter eggs scattered throughout the levels add a layer of levity to the intense combat. The addition of alien elements introduces a sci-fi flair, making the story more engaging with its unique contrast to traditional battlefield settings.

Gameplay and Mechanics

The gameplay maintains the series’ hallmark mechanics, tasking players with using firearms, grenades, and various powerful vehicles to fend off waves of enemies and alien adversaries. While controls are simple and intuitive, the dense enemy attacks and environmental traps demand quick reflexes and strategic decision-making.

The arsenal is expanded with new and powerful weapons such as the "Laser Gun" and "Flame Shot," alongside enhancements to existing weapons for greater firepower. The introduction of these options adds variety to combat and increases player freedom. The classic mechanic of rescuing POWs (Prisoners of War) to gain bonus weapons and supplies is preserved, encouraging players to explore hidden paths within levels.

Performance Improvements

One of the standout aspects of Metal Slug X is its resolution of performance issues from Metal Slug 2, such as frame rate drops. The game runs more smoothly, with improved controls that offer a more satisfying shooting experience. Level designs retain the core framework of Metal Slug 2 but feature significant refinements. Spanning six stages, the game presents diverse settings and enemy configurations, ranging from deserts to military bases and even alien motherships. The transitions between environments feel natural, with visually rich and varied scenes.

Enhanced Levels and Challenges

Enemy placements, item distributions, and difficulty levels have been meticulously adjusted compared to the original. For instance, the timing of enemy appearances has been reworked to create a more dynamic combat rhythm. Hidden weapon caches and supply points have also been repositioned for greater accessibility. Newly added nighttime settings and weather effects, such as sandstorms, enhance the battlefield's realism and add visual variety during gameplay.

Boss battles, a highlight of the series, have also been improved. Each boss features distinct attack patterns, such as giant tanks, multi-phase alien ships, and heavily armed mechs. These encounters require precise timing between offense and evasion, making each fight both intense and rewarding.

Visuals and Audio

The game continues the series' tradition of high-quality pixel art, with detailed characters, fluid animations, and lively designs for enemies and backgrounds. Explosions and vehicle effects are more visually striking, making battles more immersive.

The soundtrack features numerous rearranged tracks that heighten the tension and energy of the gameplay. Each stage's music complements its atmosphere, with the nighttime and final showdown tracks particularly enhancing the climactic moments.

Reception and Legacy

Upon its release, Metal Slug X received widespread acclaim. Critics and players praised the game for resolving the technical issues of Metal Slug 2 and for its refined enemy placements and gameplay adjustments, offering a more polished adventure. Many consider it one of the most well-balanced and tightly paced entries in the series, appealing to both newcomers and veteran players.

However, some criticisms were directed at its lack of innovation, as it heavily relied on the framework and assets of its predecessor. Despite this, the extensive optimizations and enhancements more than compensated for this shortcoming, leaving a lasting positive impression on its audience.

Conclusion

Overall, Metal Slug X stands as a classic in the Metal Slug series, preserving the original's charm while enhancing its playability and fluidity. It remains an irreplaceable memory for countless players, serving as a benchmark for 2D side-scrolling shooters. Even years later, the game continues to influence the series and the gaming industry as a whole, cementing its place as a timeless masterpiece.