I don't care how you get it, go play Aquaria. The only 2D game that's better then Aquaria is Braid, and yet very few people have played or even heard of it. It's quite simply one of the most incredible masterpieces in game design, music and art that I have ever seen. If you don't like all the exploring, then use a walkthrough, but somehow, just play the game and beat it, preferably finding the secret ending.
What is it? Aquaria is like Super Metroid, except underwater. It starts out with an emphasis on puzzle solving, moves into lots of exploring amazing places (kelp forest, the surface, a frozen lake, etc.), and then concludes with you diving deep into the depths of The Abyss, fighting hordes of horrors that will haunt your nightmares for weeks, with everything in the game being tied together in a brilliant ending to its plot.
Hints: Dashing allows you to cling to walls underwater, and repeatedly dashing/clinging is a good way to move rapidly when you don't have the Fish form.
If you don't know where to go next, its always a place you haven't explored yet, and it will always be easily accessible with the powers you currently have. The white areas on the map are the places you've explored - use the map to your advantage.
Numbers 1-8 on the keyboard switch forms.
If you get stuck long enough the game will highlight which map section your supposed to go to.
The game encourages you to look for treasures, but never adequately explains how valuable some of them can be. Certain treasures are wearable and give you things like defense bonus, and others have more interesting effects (there is a pot that gives you infinite fish meat for your kitchen).
Do as much optional stuff as you can find, because they often give you extremely valuable abilities, so valuable its often not immediately obvious that they ARE optional.
When exploring, 95% of the time there is a reason something is on the map. If you see a place or cave you haven't explored and it doesn't go anywhere, there is something valuable inside it. The only exception is when there are multiple paths to get to a location, in which case I've found that it usually doesn't matter. Your looking for places that are dead ends. Dead ends are never just dead ends; there is ALWAYS something there. Just remember that this is an adventure game, and that being curious is usually rewarded if the hordes of enemy monsters don't rip your face off.
Energy form is a viable weapon even on the very last boss. In fact, despite Energy Form being the first form you get, eating a Spicy Hand Roll turns it into the second most powerful attack in the game (THE most powerful if you go by damage per second). If you want something dead, blast it with energy form.