I thought the 'Cube GB Player would only play GBA games? Wow, I've been missing out. Now I want to find a 'Cube and a GB Player. Anyway...
Metroid II is one of my favorite Metroid games, and it's always a joy to go back and play it. The idea of a Metroid life-cycle is intriguing to me, although that life cycle has never been fully explained or even consistent:
In the instruction manual for Metroid II, it's implied that Metroids go through a series of "mutations" because of the radiation on Planet SR-388. That is, their growth cycle isn't naturally occuring.
In Metroid Fusion, this theory is somewhat confirmed, as Adam implies that Metroids can evolve to their largest stage through exposure to radiation in a lab.
In Metroid Prime, the Fission Metroids reproduce through...well, fission.
In Metroid Prime 2, Tallon IV Metroids are shown to reproduce through laying an egg-sac.
In Metroid Prime 3, Phazon Metroids are shown to lay actual eggs.
So that's sort of annoying. Furthermore, Metroids seem to have branching evolution. The radiation on SR-388 turns a "normal" Metroid into an Alpha Metroid, but the radiation on Tallon IV turns a "normal" Metroid into a Hunter Metroid? And where do Metroid Hatchers come from? It's all very confusing. Maybe, in order to get a Metroid Hatcher, you have to have a Metroid hold a Dark Tentacle and trade him?
ANYWAY.
Metroid II is basically Super Metroid without a map, which can be confusing and annoying, especially since Metroid II runs into the same problem that the original game did: extremely similar-looking environments and vertical corridors. I do very much like the inclusion of the Spider Ball, though, which eases exploration somewhat. The addition of distinct save points is also helpful, although, due to the similarities of many environments, it's easy to forget exactly where you left off! But Metroid II brings several modern Metroidisms into play: the Varia Suit, Spring Ball, Spazer Beam (tri-beam), and the modern Plasma Beam. Save points are here, the ability to go back to your ship to power-up and save, and a later level design emphasis on verticality allowed by the Space Jump.
I think the game is DYING for a modern Zero Mission-style remake. In fact, it's the only original Metroid game that doesn't have some kind of modern counterpart. Metroid got Zero Mission and a ton of ports and Super Metroid got the VC treatment. Nintendo seems to have forgotten about Metroid 2...which is why I'm very excited about the Metroid 2 Remake Project:
http://metroid2remake.blogspot.com/