The mechanic is interesting, but Blizzard uses it in bad way ( Expensive minions with bad stats that recruit smaller minion )
You also have expensive minions with bad stats that recruit bigger minions ( Silver Vanguard ). And you have expensive spells that recruit any minions ( Gather Your Party ). And you have reasonably costed minions that recruit specific minions ( Kathrena Winterwisp ). There is a Little bit diversity with recruit. The only Thing we do not have in this set (yet) is a reasonably statted minion (with regard to teh cost) that additionally recruits something. Because that would likely be too strong.
So I personally don't like it. That is not to say it isn't good. Y'Shaarj, Rage Unbound is such a must have in EZ Big EZ decks because in the right card it can be a very strong mechanic. I'm fun with one or two cards like that, but I believe it should not be as common mechanic as K&C is making it.
I don't like the RNG, High-roll and deck building restriction on it. Now the RNG and High-roll most people understand why it should not be the foundation for tier 1 decks. Deck building restrictions is seen by many as fun, and challenging. Which they are.. for the one guy who does the deck. Then everyone just netdecks that deck, and well... all you just have is a very strong deck. If you have a Tier 1 deck with a building restriction (Prince Rogue), maybe with Eviscerate it will be Tier S, but at the end it is just like any other Tier 1 deck. Very strong, and that's it.
Only aspect I like about recruit is that it forces you to play more minions based on their stats and deathrattle (ie more board orientated) and less about battlecry. I think battlecry is just a spell that forces you to have a minion then on board (nicer than the spell, as it means you care more about the board). In this way it encourages minions like Tar Creeper and less Bonemare. So that is the only aspect I like about recruit.
I actually don't think recruit is a highroll mechanic. In my understanding, it is the opposite. It will make your draws more consistent after the recruit.
Of course, if you just slam a recruit Card (lets say Guild Recruiter ) in any normal midrange deck, the results are from bad (1 drop) to very good (4 drop). But when you adjust your deck, lets say a druid, and you play the recruiter, then it pulls a 4 drop from your deck (or maybe the Greedy Sprite ). Oaken summons will do that as well, while giving you armor. Recruit Cards are basically reducing the deck size by one per recruited minion helping you getting to your other Cards while teh Plays can still be impactful. Admitted, you can low roll by having drawn all 3 or 4 Drops from your deck when you can play the recruit Cards, but that can be controlled by deckbuilding.
High roll is hoping that barnes pulls Highmane in a regular midrange hunter deck. If you have no 1 and 2 Drops in your deck, you will know that you can only pull 3 and 4 Drops with guild recruiter. If that is still too highrolly for you, then cut the 3 Drops (in Druid that is possible). And afterwards, you will more likely draw your endgame stuff like.
Edit: Btw. I don't think that recruit leads to less bonemares, I think it leads to a more consitent draw of bonemares.
The mechanic self is busted. Patches the Pirate is essentially a recruited Card (value and tempo for free + deck thinning) and he made pirates a staple of every half aggressive deck. If you give Guild Recruiter 's effect to a chillwind Yeti, he would be insanley overpowered.
And that's why all the recruit minions and spells are so heavily overcosted. I guess there will be some playable ones (I personally think guild recruiter could be one, Call to Arms also and maybe Oaken Summons ), but the new minions/spells with recruit are weaker than for instance Y'Shaarj, Rage Unbound or Mad Scientist.