Here's a question... Why has the Megaman style of side-scroller never branched off to something other than Megaman?

My thoughts, use the Megaman (1-8) style engine for a different franchise, specifically Aliens or Aliens vs Predator. AvP works best as the "player" could be a predator, and his shoulder cannon could be the equivalent of Rock's Burst Cannon.

Picture your pred in the selection screen, centered around eight different "special" forms of xeno (the bosses). Select your level, fight your way thru to the boss, and for defeating him, gain a new cannon power. Slight changes on the Megaman approach, your new weapon won't be the power of the boss defeated (wouldn't make sense), but by defeating a boss alien your Predator superiors reward you with a cannon upgrade or ability. Abilities would be things like Invisibility Cloak or Thermal Vision Helm, using these abilities would consume "power" like any other cannon shot, but while equipped your main cannon is the normal shoulder blaster. Obviously, a separate button would be set aside for the secondary abilities.

As with any Megaman game, after the eight bosses are 6-feet under, its on to the final boss's lair (3-5 levels), and who do you think the final boss would be? If you didn't say Queen Alien, go sit in the corner.

As for the rest of the game, the non-boss "enemies" would be weaker alien forms, face huggers, and maybe even the odd rival Predator. Give the game a darker feel like Abuse, but keep it within the cartoony realm for fun. Could also open the door to countless sequels, meaning not only we get some wicked games (for once), but this could revive the Aliens franchise too, with plenty of new Xenos to see.

Thoughts on the possible weapons earned for the first game...
Basic Gun "Blaster", unlimited use.
Boss 1 - Throwing Disc (Think "Metalman")
Boss 2 - Spear (short-range stabbing action, very high damage. Not good against ranged-attack enemies)
Boss 3 - Thermal Blaster (Fire, grenade-like lobbed shot)
Boss 4 - Cryo-Blaster (Ice, conical attack)
Boss 5 - Electro-Blaster (Don't Tase Me Bro, straight shot)
Boss 6 - Stealth Cloak
Boss 7 - Pulse Blaster (fires in a vertical spread pattern, weaker shots but good coverage)
Boss 8 - Thermal Vision (shows secret paths, hidden enemies, and otherwise invisible powerups)

As with ol Megs, some of Pred's alternate powers would be more effective on certain bosses, others very weak. Definitely throw in at least one "Instant Kill" like MM2/3.

Anyone else have other ideas to expand this game?

um...no. I think Megaman meets Metroid Prime would work though. Freeroaming FPA but still the rock paper scizzors bosses.

On a semi-related note (since you mentioned the status of the Aliens franchise), there is a new Aliens game coming out that looks pretty sweet. It's an fps, but still, it's an Aliens game.

And, no offense, but Abuse pretty much already did what you're thinking of, in my opinion.

Speaking of Aliens.....where is Alien 5? We need a reboot to get rid of 3, Ressurection and the AVP movies. Make a good scary one again. Let it die on a good movie, not these....things we've been given.

Aliens 3 was good, just wasn't AS good as 1 and 2. I'll admit 4 was a letdown, but I loved AvPR, and AvP wasn't that bad.

This actually sounds a lot more like Super Metroid. Except, you know, you aren't guaranteed a new power after every boss.

/offtopic God, I wish every Metroid game after SM didn't suck so hard.

Re: this being the same as Abuse. No. Abuse was a mouse-aimed shooter, Megaman a sidescrolling platformer. I'd love to try this as a platformer.

Re: Metroid... This will probably get me murdered here, but I haven't played a Metroid title since the original NES one, didn't much like it, made me too jumpy because of the music.

Trust me....the Metroid sequals are better. Much better aiming and it's not as hard to get so lost you commit suicide just to get to the entrance of the area.