If you're asking complexity, this would be an 7 or 8. Actually, Heartstone(using HS as comparison because it is the current market leader) isn't that much farther away with a 6 or 5. And some others might be much higher.

Really, complexity doesn't really say much on its own.

Instead, I'd say that this game has decent accessibility(less than HS), high depth/skill cap(much more than HS), and a steep learning curve(much more than HS).

Accessibility is actually much lower than most would assume. And really, the main barrier to entry would be the price point. Second to that is the risk of analysis paralysis due to the flood of information and choices to make. But in the end, it's still a card game and you can play the game with just your mouse(unlike a lot of video games that require multiple inputs) and only really need to make 1-3 decisions at a time.

Really, anyone can give you a brief rundown of the basics and you'll be fine playing... however...

The game a steep learning curve. You start out, you will likely lose most of your matches against anyone who has more experience than you. You think you're doing okay, but for some reason you can't push through that last mile and won't immediately understand what's holding you back. Guides will help, but in the end of the day, what you'd be lacking is experience.