As someone who played in the semi's against CLG (roaming HS taric made me sadface), there are a few key things that CLG did that should be noted.
1. Their pregame is impeccable. They banned what they didn't want to play against (zil, shaco, rammus) and chose champions based on this comp:
Solo Top: AP Carry -- jiji on Kass
Solo Mid: AD Carry -- Chauster on Ashe
Farm Independent Roamer + Strong Farming Solo Bot: HS on Taric + Elementz on Sion
Jungle: Kobe on Nunu
Our comp was:
Xpecial as Kennen top
Neverlike as Corki mid
Itzkill as Alistar (roamer) bot
Ralk as Gragas bot
Me as Olaf in the jungle
Comp-wise, we thought we planned our pregame well. Corki should beat ashe mid, kennen should zone kass early, alistar is a really strong roamer, gragas is a really strong laner, and olaf will just blast through all their cc mid to late game. However, there were very specific things that CLG planned out that countered us in practically every lane. These elements were so specific it would be hard to tell without really looking through their setups. For example, rune setup on Chauster's Ashe. We didn't really check them specifically, but we were sure, after like 3 minutes, that he was running flat MR runes vs. Corki which severely weakens Corki's phosphorus bomb harass. Simple things like this, allowed CLG to play exactly what they needed to counter us.
2. Their control of the map is really (too) strong. Kobe invaded my jungle by taking my red. They forced me out of my wolf camp without taking it (4-5 of them were there with me by myself). So I started at little golems/wraiths. Using clairvoyance, they noted when I was on the blue side of my jungle. So I asked my teammates to scout for me while I took blue which accelerates my jungle. By this time, Kobe already had blue and invaded my red and repeatedly harassed top at level 2. He was unsuccessful and relatively behind as a result. But this was about the time when HS had enough gold for an early oracle and boots destroying our map control and roaming like no other. This roaming aspect is something our team acknowledges is a skill we lack. Once they got that early control, the game just snowballed out of control.
There are probably a lot more intricacies to CLG's play that we're missing, but these are the biggest factors that we believe lost us the game.