The first game is as good as Super Mario 64 was on the first day of its releae in terms of innovation and level design. Grpahically, it was not superseded on the Gamecube except by MP2, and the music/sound is great. The gameplay is the only FPS I've ever felt natural with, and yet the Super Metroid sense of exploration and reward is perfect. It's my favourite game ever, and I only buy Nintendo games.

Since Metroid games are story-light, no, you do not need to have played the first one to understand it. MP2 is more of the same, but as it isn't "new", it feels more repetitive (only compared to Metroid Prime - it's still a masterpiece)but the graphics and engine recieve slight upgrades from MP.I would say you should play the first one first to experience the shiny newness, rather than to understand the second better.

Zdub, NMH

SUper Mario galaxy

Why a classic controller?

You can just use the GC controller.

Eternal Darkness,
bought it for only $20 and its worth it :)

Luigis mansion!

 Two isn't as good in my opinion, although I'm hard pressed to explain why, to be honest. I will give it this, though: its boss fights are easily the best in the series (Metroid, not just the Primes). 

As for your original question, you can stretch your dollar furthest by getting Zak and Wiki ($20, Point-and-click...Puzzle Game?), Baten Kaitos Origin ($20-$30, long RPG), Paper Mario: The Thousand Year Door ($20, get it no matter what), and Okami ($40, Long Zelda-esque game). Alternatively, you can get a bunch of Wii Points, and buy some of the myriad of Virtual Console games out there. You might also enjoy Lost Winds ($10), although it's a tad short, and I didn't like it as much as most others.  

Wiifit or SSBB.

Tell us what do you own.

No More Heroes.