I'm actually a huge fan. The animation looks DAMN good while still being colourful. Characters act similarly to how they do in game without overusing the cartoonishly exaggerated spell effects. While the overall "story" of the game isn't shown, it pulls a Team Fortress 2 in focusing on the personality of the characters, and with a few exceptions (Ahri, maybe Ajani) they manage to make them expressive WITHOUT dialogue.
There's even a few little touches, like Zyra dropping plants to block an incoming skillshot, Darius using the hook on his axe to pull an enemy closer to him, Jax doing a little spinning parry with his lamppost... even Nautilus popping his shield and trying to use his hook ability to escape when faced with massive incoming damage.
Sure, it makes the game look crap by comparison. And I'd prefer that more work went into reworking old or broken champions (Hello there, Poppy and Sion!) rather than creating new CG trailers. But hey, it looks cool, it lets the animators show off, it's a nice bit of fanservice for all the people wanting to see their favourite champions and could serve to attract a bunch of new players to the game.
(Also, I'd like to remind everyone going "this is nothing like the game" that our dear friends at Rito noticed that too. [http://youtu.be/WPDtBsQsxV4])