*Ahem* I like this topic. I'll note the things I like about a few of my favorite scrolling shooters:
Gradius - the power-up system enriches the strategic elements; the options (AKA multiples) can be used to either spread out your field of fire or concentrate your firepower; the Vic Vipers all look awesome; Weapon Edit mode is fun stuff; I like Gradius' music enough that I own the Gradius Arcade Soundtrack on CD (Gradius I-IV music); Boss Rushes; engaging, diverse boss battles; one of the best features in Gradius V: credits get added for each hour of play, eventually leading to free play (I beat the game before free play in Easy mode, but Normal would have been impossible for me); Gradius V lets you practice stages (that you have already reached) separately from the whole game. FYI, Gradius V is one of my all-time favorite games.
Darius - the series has such a distinctive look to the enemies, particularly the bosses (namely, that mechanical sea life look); the branching stage structure enhances replayability; Zuntata's mind-warping, otherworldly music--I don't have any early Darius soundtracks, but I imported DariusBurst's and the just-released DariusBurst Remix, which I'm listening to right now; the later games have very wide boss diversity (look up Titanic Lance, Dimension Diver, The Embryon, Mirage Castle, Dark Helios); picking up more shield power-ups increases the number of hits you can take, at least in DariusBurst; G-Darius' alpha/beta beam boss dueling really heightens the tension; DariusBurst's Burst Cannon not only can function as a remote weapon, powerful blast, and even a defensive barrier, but also as a beam-dueling device; lastly, have you seen DariusBurst's incredible prerendered promo trailers?! :)
R-Type - The Force and properly using it make for an extremely tactical experience, compared to your typical scrolling shooter; some other scrolling shooters also have this "indestructible remote weapon" concept, like Xexex and Last Resort; the Giger-inspired look is not really my cup of tea, but it is distinctive.
Xevious - the secrets (Sol Citadels and Special Flags) hidden all over the place really make exploring the world pretty interesting.
194x series - er, I'm a big P-38 Lightning fan . . . in retrospect, these games didn't really have all that much distinctive stuff, did they?
Castle of Shikigami - I can't say I really like these that much, but the multiple character stories (different single-player endings and such, even endings depending on who 1P and 2P play as), coupled with some crazy dialogue, are kind of fun and act as incentives for replays; also, I think the Sengoku Ace series had something similar; this series also rewards you (score multiplier) for being close to enemies and enemy fire.
Everyday Shooter - every single stage has unique gameplay; the visual/aural style is psychedelically striking.
Ikaruga - I never got far into it, but the polarity system really kept you on your toes.
Space Invaders Extreme - makes Space Invaders fun for me: entrancing audio-visual beat.
Parodius - you're on drugs the whole time.
SeGaGaGa - I don't actually know much about this Dreamcast game, but there is a space shooter mini-game at the end composed of a boss rush--against Sega's game consoles from years past. This probably isn't something you could do in your game, though.
I think adding some sort of tactical element to the gameplay (along the lines of Gradius, R-Type, and DariusBurst, when "properly" using the Burst Cannon) really makes a scrolling shooter stand out. Whether it's for getting a better score or just plain surviving, requiring good weapon management enhances the player's reward response (i.e., makes the game feel more fun when you do well). This is particularly true for boss battles, the big showpieces that stay in mind afterward. Also, visual distinctiveness helps burn a game into people's memories; one look at The Force, or 4 options following the Vic Viper, or a giant mechanical space sperm whale packed with weapons, and you remember which game that was.
Things to avoid:
- losing all power-ups once you die, coupled with making the game impossible to play without said power-ups
- making foreground (obstacle) and background (harmless) elements difficult to distinguish
- making the player's base weapon so weak even the lowest enemies take a bunch of hits to kill
- forcing a level restart if the player dies, or using checkpoints spaced far apart in a level
- lack of autofire; it's not that bad in general, but on a portable system, repeatedly smacking a button shakes the screen
- hitbox bigger than the player . . . seriously, I've seen this before
- Engrish . . . actually, this could work for you! After all, you already misspelled "FuturLab"!
I don't think being "short" is a problem if the game plays great. One run through Gradius V takes like 85 minutes; one run through DariusBurst is like 35 minutes; heck, Slap Fight starts repeating the areas about 11 minutes in. Gradius V is helped out by its being really hard (especially Stage 7), and DariusBurst has the branching stages and extra game modes to extend its life. As for Space Invaders Extreme (which has branching stages), I've never beaten the hardest final stage, so while pspgamer01 thinks it's short, it's taken me about 2 years so far. :)
Oh, one more thing I've always liked about Darius: "WARNING! A HUGE BATTLESHIP $boss_name IS APPROACHING FAST!"
I'd happily be a beta tester for you, by the way!
