This is a sensitive subject with people (and pretty polarizing generally), so I thought I'd speak to this a bit.
Our goal is to make sure we're offering a variety of archetypes, but like I was speaking in the other "grotesque" subject thread, we're not interested in making stuff that has the sole purpose of showing how clever, different or creative we can be (bee void champion you mention). Our goal is, instead, to make stuff that our players want.
What does that mean?
* Players want some sort of fantasy fulfillment. That fantasy can be a badass killer (Tryndamere), ironic juxtaposition (Annie), cute underdog (Teemo), world-ending monster (Cho'Gath), and tons of other methods of fantasy fulfillment.
* Players want variety. Since each player has unique tastes, every champion won't be one they like - that's not our goal. Instead, we want to make sure each player has several releases they can get interested in. This includes humans (Fiora), stranger creatures (Nautilus) and whimsical characters (Ziggs or Lulu). Just this year, there's plenty of different archetypes and themes available.
* Players want to understand why they should play a champion. Anyone should be able understand what they're getting by seeing the champion's art, theme and ability set. Clear sources of power and cohesive packages help make sure that it meets expectations and shows off why a champion is exciting to whatever audience it's intended for.
What is not important to us when choosing champions?
* Being different just to show we can. Like I was saying earlier, very few people (yes, and this is testibly true) actually care about this. I'll go so far as to say I think designing with this as a goal is unethical and masturbatory - a developer's duty is to the game and the players, not ego and pride. Uniqueness is only a goal in how it serves variety.
* Exploring every possible rare niche. We could make some crazy thing you've never seen to satisfy the idea that nothing is off-limits, but frankly, some things are. We won't make a Balloon Animal champion, or a Spaceship champion (skins, however...) because they don't make since in our game, our world, or to the vast, vast majority of people who play League of Legends or ever would play it.
If you don't like Darius, then that's fine! It's easy to choose to not get him or play him! It's your right to expect champions you like to be released at a reasonable cadence. It's not realistic that every champion is designed with your individual tastes specifically in mind, or that anything that you don't like personally means that no one else will. We study and think about this a lot - I personally invest a ton of time, passion and work into doing this, as do a lot of others.
I'm really excited about Darius, especially because Sion does not fulfill the experience of an awesome guy who has an axe-based fighting style, and Darius most certainly does.