Really? It's quite a bit a bit different to the other Jak games. The main bad guys are Gol and Maia (they are Dark Eco enhanced freaks. Your 'main' enemy is the Lurker race. You have no weapons at all, but eco will help you through your quest:
Green - Collect and you regain health.
Blue - Increases your speed and you can activate precursor objects (lifts etc.).
Red - Increases your strength, you can also break down certain things.
Yellow - You can shoot blasts of energy that will track weakly enemies. You can also aim by going into first person view.
Dark - Death, DO NOT TOUCH.
Light - Super powerful (I won't say anything else).
In this one, precursor orbs are EVERYWHERE. You use them as currency here, usually for purchasing Power Cells, which are the most important artifacts in the game. You really should get it as soon as possible, it's a great game!