Colony is on my top 10 list of favorite songs (video game or otherwise -- and it's actually the only video game tune on there!).
Weaponwise, I think all the weapons have their uses. The straight laser is pretty powerful, but I think the round vulcan provides a lot of flexability on non-boss enemies. The boss at the end of stage 2 -- I think one of the bomb weapons is useful here (when he walks towards the left side of the screen). Even the morning star may find some use taking out large numbers of small enemies (unfortunately it's not available for the opening of stage 1, but it has its uses in the lava stage). I think the weird ass lasers you get for the last mission may be optimal as well, since you can hit stuff on the opposite side of ships with them. Very unwieldy though.
Overall, I think the only useless weapon would be the Needle Cracker.
Anyway, about the gameplay mechanics themselves. I think there are a lot of interesting things that could be done that a normal player wouldn't do because they're too hazardous, including:
Stage 1:
Go horizontal through the floating shooting rock islands, trying to destroy them all, as well as their debris.
Go very quickly between the tunnels towards the end, trying to take out extra enemies before having to commit to one tunnel.
Stage 2:
Wait until the last moment to pass under the blocks that fall after you shoot the supports out.
Stage 3:
Go in and out of the pipes over the city, trying to destroy all the cannons.
Stay inbetween lasers when they are shot at you by both bosses.
Stage 4:
Leave the jellyfish creatures attached to your ship (if I remember correctly, they just drag the ship down)
I'm sure there are some other ways to spice up a run like this too. I know after you beat the game, it puts it on a harder difficulty -- I don't know if you can skip to this harder difficulty automatically, but if you can, that would be really cool. The amount of bullets that come at you in the hardest difficulty surpasses anything like Gradius.
