I approve of 8 out of 10 Guild Champion Runners

Interestingly, that's how many we've seen so far.

I hear complaints about cost, mostly and all I can think of is: but they do awesome things! The have to cost that much in order to not break the game in two.

Exava gives the Rakdos cards the real boost they need to be a considerable threat, in addition to being a good one herself.

Lavinia is going to be a house and a very annoying one at that. She will be flickered and, in the style of the old Prison decks of yore, leave opponents wishing that the game would just END already.

Melek looks insane. It is free spells plus extra cards. If it didn't cost six mana, no one would run anything but blue/red.

People were complaining about Mirko because 'it's weak and overcosted.' These people have never cast Mind Funeral. My average when I cast Mind Funeral is about eleven cards. Casting Mind Funeral every turn for free? The only reason it doesn't look good is because Blue can't protect it well in Standard. But I don't care about Standard and in nearly every other format, Mirko has potential.

Ruric Thar has already been covered on The Magic Show. Essentially: I agree with this. (TAKE 6 TO THE FACE!)

The complaint about Teysa is the same one people have of Mirko and I just have to wonder: what is wrong with these people? She's a vigilant No Mercy that can generate tokens. How could she cost less? And doesn't Teysa just take over combat, once she's on board? That's pretty amazing for seven mana.

Varolz is the most boring of the Runners. He doesn't interact meaningfully with the previous mechanics of his guild, he just provides all creatures with the guild's ability. Meh. That said; he's cheap, he's difficult to get rid of and it's not hard to imagine a deck using him which may provide the BG guild the attention it needs.

Last is Vorel and I'm just thankful that the uber-proliferate card didn't come out in Scars of Mirrodin block. That would've been very bad. As it is: that card is going to be a lot of fun for people and (thankfully) he doesn't interact with Planeswalkers because then he'd just be broken.

I'm less enthusiastic about is the Fuse mechanic. I appreciate the elegant way it connects back to the last Ravnica set and solves problems like: how do we show the guilds are linked or how to we make sure there are enough cards representing each guild? However, as a mechanic it's simply Splice from Kamigawa block and it doesn't even allow you to mix and match to the same degree so it's more restrictive. Finally, the flashy cards that might make people want to play it are expensive, without providing justification for the expense. Eight mana to put four fliers and draw four cards (on Beck/Call for example) is quite good but it doesn't break the game.

Also, as with the Apocalypse split cards, so far: the blue/red one is clearly the best. That is probably only objectionable to someone who has been playing for 18 years, though.