"I spent a lot of time on the different attack styles. There are so many ideas that didn't get through the proposal stage but I think everything came out satisfyingly well. The company's female colleagues play-tested the game with their eyes shut complaining "[they] can't look at it straight it's so gross!"" The boss fights were also made deliberately huge and repulsive at the request of Uchida. "Getting the enemies right is 100% important. There is a formula in Hollywood that says a movie will be a huge hit if you manage to create an incredible villain. This applies in the same way to games".
Perhaps inspired by a famous film released years before, the trio call themselves Alien Busters, and despite looking different all three heroes seem to handle identically. It's a shame as other games where you move across the screen fighting an endless stream of foes feature characters that behave noticeably differently. 'Streets of Rage' and 'Final Fight' for example offer a diverse cast and choosing the one that best reflects your play style is key to success. However in 'Alien Storm' Karen, Garth and Slammer all move at the same rate, run and tumble at the same speed and offer the same attack range when fighting foes. Though each character uses a different style of weapon, it turns out to just be a cosmetic difference and if the Internet is to be believed "they're all running on the same engine under the hood".
Both were released in arcades using similar hardware and both were ported to the Mega Drive to satisfy Sega's claims that they were bringing the arcade experience home. 'Alien Storm's Garth even looks like 'GoldenAxe's Ax Battler, only in futuristic clothing. Both games are presented in a 2.5D view which allow players to move in and out of the screen. "We had seen the 2.5D view used in other games and chose to adopt this approach" remembers Uchida talking to Keith Stuart In the 'Mega Drive / Genesis Collected Works'. "However this decision tremendously increased the amount artwork required" recalls the game's designer. To increase the sense of depth the backgrounds in 'Alien Storm' employ the classical Trompe-l'œil effect: an optical illusion that fools the brain into perceiving depth on flat surfaces. The streets that seem to vanish into the distance are there but the perspective doesn't change in relation to the character's positions. "'Alien Storm' is virtually arcade perfect! The graphics are spot-on with a whole host of brilliant aliens and decent backdrops" suggested Richard Leadbetter. Side by side the arcade and mega drive versions do indeed look similar especially the sprites. The backgrounds on the home port are marginally less varied and the level transition animations have not survived the journey home but otherwise it's a faithful port. Comparing the audio is less complimentary to the Mega Drive version; the sample speech has all gone and the sound effects are confusing, far too loud in the mix drowning out the music. Not that the background tracks are that special. They're noisy, repetitive and tinny but that seems to be in-keeping with the gameplay.
It's all reminiscent of 'Operation Wolf' and a very similar mini game was also a part of the developer's earlier output, something game designer Makoto Uchida admits to. "They were inspired by 'Shinobi' which was created by my senior. That title also featured a first person bonus game which I referenced in 'Alien Storm'". But while they provides a change of pace from the scrolling fighting, some reviewers believed the sections to be so badly made that you'll miss the main game. Dan Whitehead even called them "atrocious shooting gallery stages" when he reviewed the digital re-release for Eurogamer. "Collision detection is fussy, meaning you have to be on the exact same horizontal plane as an enemy to cause any damage, while the treacle-slow cursor pace does little to keep you engaged".
Perhaps more successful are the "endless runner" style levels in which your character is constantly moving towards the right side of the screen almost like they were in a scrolling shoot em up. Along with shooting you can leap over enemies and change your position relative to the constantly moving ground; not unlike the infamous speeder bike stages in 'Battle Toads'. Uchida believed frequently changing the style of play was essential to keep a player's attention. "If the gameplay is intense for more than a few minutes they get tired [...] Apparently our concentration levels go down if we watch TV constantly for 15 minutes so we also felt it wise to insert something like a bonus stage every 15 minutes too".