This is probably one of my favorite Pokemon games ever. The Ranger stint just works for me, better than the traditional Pokemon games. It's just more interactive and quite challenging too.
The game play is a lot different from the other Pokemon games since your character's a Ranger and you capture and befriend Pokemon not to battle, but to help you accomplish quests and missions.
You don't need a Pokemon to catch other Pokemon. You'll be given a Styler that you'll use to capture a wild Pokemon (or to save Pokemon in some cases) by drawing loops around the Pokemon. The creature can and will attack sometimes and if you're not too careful, your Styler will break and it's game over for you. Or you can just go back to your last save point.
You can use the Pokemon that you captured, aside from capturing other Pokemon, to clear out obstacles to help you get through the game. These are called Poke Assists. There are a number of Poke Assists that you will find familiar: Tackle, Cut, Soak. Then there's Recharge that will fill out the energy gauze of your Styler so you won't just die or something.
The plot itself is quite engaging. Simple story, yes: as a Pokemon Ranger, encounter bad guys who use Pokemon to take over the Almia region. For something that simple, I was amused throughout the whole game that I couldn't really put my DS down.
Now to resume playing Pokemon Ranger. Yes, a different Pokemon Ranger game lol XD