How difficult is this game to learn?

I don't know about the tutorial, but if you play Civ you should have no problem grasping the concepts of this game. 

4x, city management, and diplomacy won't be new concepts for you. In addition you get tactical combat (played Master of Magic?) and quests.

A love for the fantasy genre is probably also needed.

There are a fair amount of easy difficulties no matter, so if you are having a hard time you can help yourself with setting down the difficulty.

The tutorial will not explain to you how to "win the game", you have to figure that out by yourself (as of right now), and some of the better tactics is slightly more difficult to grasp.

So what I am trying to say is, if you don't want our advice, and want to experience the game on your own, to be successful you will probably need a keen eye for the imbalances in the current game, or just enough time with the game.

For my head it didn't take very long to learn the game, but I have a head for games and systems, so I grasp these things easily. And if you have played CIV 5 you will also grasp some of the core concepts easily,
for example: I have a city, my city can produce units, and construct buildings.
Some of the other concepts will get some getting used to, like putting enchantments on cities, and changing taxes, but we can't go making exact replica's of other games now can we?

It might help waiting until the game gets out of beta, if you don't want to participate on the forums. Since that should be a much more polished game.

Whatever you choose, good luck

Sincerely
~ Kongdej

The tutorials teach the basics of the game with video walkthroughs of gameplay (and a lot of them), which is a really nice feature for the uninitiated.

Like Kongdej said, I would wait for release if you want a more stable experience that's not shifting gears on you every week or so.

The tutorial won't tell you much about the entire game. It just shows you "currently" at least that you can settle a city, build buildings around you city, research things, explore the map, pick up goodies on the map, build outposts to capture resources, hire heroes, fight monsters. Also, a quest shows up, but it doesn't talk about it and you are not required to go on it yet.

From my understanding the tutorial will receive some fixing in the upcoming weeks so it will change.

For the game itself, there is an extreme amount of depth to the game. It is difficult due to the amount of things you can do. Ever play D&D or a role-playing game like NWN. You have dozens of traits and things to choose from and figuring out which combo's work for you and don't work for you is something that couldn't be told because it doesn't fit some peoples play style.

It is easy to figure out what to do, it is rather straight forward in that sense. I got bored of Civ 5, because it just wasn't enough for me. I find that I can play the game casually and survive pretty well and have fun doing it. Do I always win with the strategies that I choose, well no. But it was fun to experiment and play.

If you like a beta experience then you should pick it up and get in on the action. If you don't care much for the experience, then well maybe you should wait till it comes out in a few weeks. I have never regretted this purchase, but then again this game is not for everyone either. I find it a nice blend between strategy and rpg for my tastes.

Harder than CIVIV, easier than ES. 

My guess is endless space