Differences Between Christianity and Asatru

At first glance, there would seem to be many differences between Christianity and Asatru, but many of these are superficial. At the heart of the matter are a few core, fundamental differences in how we view people and what makes them special. Fortunately, these differences are easy to explain. Unfortunately, the differences are hard to argue in a religious debate.
Christianity is, of course, derived from the religion of the Hebrews. At one time, the Hebrews believed they were a specific people with an agreement with a specific god. As long as they kept up their end of the deal, their god would keep up his. They did not seek to bring in more followers because you were either one of them or you were not. It's my understanding that modern Jews share this belief and usually do not take in converts.
With the advent of Christianity, the goals changed. The new branch of Hebrews wanted everybody to join. One of their foundational beliefs is evangelism, meaning that each member is required to try to convert an many non-believers as they can. By doing this, they grew their numbers relatively quickly, once they got started. Note that their Muslim brothers share this characteristic.
The main strategy for conversion involves a narrative about people. This story that describes people provides a motivation for joining (ignoring the historical violence used to force conversions.) The narrative hinged on several points:

• Humans are inherently flawed due to Original Sin (Adam and Even fouling up in the Garden of Eden).
• The Christian god wants to forgive people, but the people have to agree to dedicate themselves to his service.
• Everyone is effectively equal in the eyes of their god, so you don't have to do anything other than believe in him and do as you're told.

In Asatru, however, there is no concept of original sin. You are born human and, like all human, you will have various strengths and weaknesses. Your path starts where your ancestors left off and leads, for the most part, where your efforts take it. This happens whether you believe in the Gods or not.
More importantly, not everyone is born equal. For any given task, there will be some who have a weaker talent and some who will be stronger. Effort can change your skill level, relative to one's talent, but it takes both together to finally reach one's peak. Statistically, there will be some people who have more skill and talent in general, and there will be those with less. It makes a spectrum of strengths and weaknesses. Things just work that way. (NOTE: This spectrum applies to people of all races and ethnicities; don't let racists tell you it doesn't.)
Because each person is different, it is up to each person to build their strengths and minimize their weaknesses to build themselves to serve the Gods. By being a productive member of society, to the best of their ability, each person contributes in their own way. Each could be seen as special, but we prefer to see each person as unique. Making the effort is a respectable activity!
Punishment and Afterlife
Christians enhance their evangelism with the added threat of punishment in the afterlife. They say that you will be tortured forever once you are dead if you do not join them. Of course, they also list an assortment of bad behaviors that will also lead to punishment, but those can be forgiven through absolution at the last minute. This seems odd to non-Christians, but it seems to be well ingrained into the religion to varying degrees through their sects.
Asatru does not have a punishment in the afterlife. Instead, the parts of you that move on will find themselves in the company of similar beings. If you were a farmer, you will be with other farmers. If you were an adventurer, you will be with other adventurers. However, if you were a backstabbing scoundrel, you will find yourself with other backstabbing scoundrels. This is more akin to finding someplace with which you naturally resonate rather than being a punishment or reward. Those who live their lives acting like venomous wyrms will find themselves resonating with venomous wyrms in the afterlife, not because it is punishment but because that's where you fit in.
Evangelism
Christianity demands that its adherents spread the word. They want to convert everybody and then some. In the big scheme of things, they would prefer that there is no other religion in existence. Fortunately, like most viruses, it has mutated as it spread, so many of them are less effective at spreading the faith, and many other people have built up an immunity.
Asatru does not require that other people believe, though there is nothing wrong with encouraging the religion. We are prone to recommending proper action, regardless of your motivation, because honorable actions add to the wholesomeness of the Nine Worlds.
There are some who think that Asatru should not be spread. I'm not sure why. For some, it seems they equate such activity to Christianity and find it distasteful. For others, it seems like they want to feel special by belonging to a smaller, more exclusive group. I think we are better off if more people actively serve the Gods. It makes it easier to maintain the conversations about what serving the Gods means and it makes it easier to encourage wholesome behavior.
It is worth noting that most Asatru people today are fully aware of the historical interactions between Christians and non-Christian people. As a result, we tend to have our guard up and are ready for the bouts of violence inherent in a religion that requires conformity.
Conclusion
The main differences between Christianity and Asatru are that we think you are fine and that you don't have to believe the same things we do. If you think it makes you more special to kneel before some god that only ever appears as fire, that's fine as long as you don't bother us with it. When you go to the afterlife, where you go will still be dependent on your nature as a person and not on what you believe.
With all that in mind, it is up to you to decide whether you are a candidate for automatic, magical "saving" from some supposed ancient sin, or whether you prefer to revel in the challenges of life and stand tall with the Gods.