I've been wanting to get into Strategy games and I've heard good things about this one. I've been looking at this game on Steam and I'm trying fighting back the urge to make this an impulse buy.  Do you consider this game too difficult for someone new to RTS?

I've put more hours into this game than many others.  Like Shirogane says, the campaign is awesome... both in the original and the expansion.  Last Stand is also a lot of fun.  Its really easy to jump into and gets very exciting and tactical at the higher waves.  The ranked multiplayer is fun if you can hang with the guru's that you have to play against (I certainly can't).   
 
This game is much more tactical than a traditional RTS.  Now that I've been playing it for a year I actually prefer it, and I can't really picture myself going to back to a traditional RTS and enjoying it like I used to.  Last Stand and Campaign mode both do a great job of scratching the loot collection itch if you have one.   
 
I can't recommend this game enough.

n00basaurus needs a medal because he's spot on.
 
The gold edition is pretty much a steal.  $40 for two great campaigns in one of the most advanced tactical games out there.