I don’t think I have to tell you which one is new.
Most of the items in Metroid Prime are taken straight from Super Metroid (the latest Metroid game when this was being developed), but with new takes on them to adapt for the play style, or in this case, new upgrades particular to them. One of the less-used mechanics of Super Metroid was Charge Beam combos. Essentially, if you have Power Bombs active and charge your shot while only two beams are selected on the status screen, then it just activates automatically and takes a Power Bomb away. It’s a way to make Power Bombs more combat-friendly, but it’s so hidden that most people don’t ever bother even if they do know it exists. The Charge Beam combos in Metroid Prime are much easier to use, but rather than Power Bombs, they just use a lot of Missiles. Super Missiles are the only ones useful outside of combat, so they use less, but they also do less damage. That said, the “less damage” is still significant enough that it’s rare for other combos to be worth it.
As beams are not simply upgrades on the standard Power Beam in this game, they each have something special about them. Ice Beam has the lowest fire rate but does the most damage, destroying most objects on just a normal hit rather than a charged shot. It also freezes some foes on a charge shot, or for Metroids, with a normal shot. Since you’re never required to platform on frozen foes in this game (in fact, I believe you can’t stand on them), it lacks the property of not killing freezable foes that it had in Super Metroid. Overall, it’s very strong, but that low fire rate is killer and I generally won’t use it in combat unless I need to do so.