If it is important enough for Jesus to have repeatedly taught on it at length, it is important enough to take Very Very Seriously as a theological point.
Literalists aside, there is plenty of room for doubt / ambiguity re exactly what Hell is.
The odds are remote bordering on non-existent that it is an actual place in the Universe as we know it.
More commonly, it's taken that Hell / Gehenna represents a condition, not a place. It is a separation from God, not a banishment, certainly not a punishment in the petty human tit-for-tat concept.
Rather, it is self-inflicted.
Christianity holds that we are a broken people, that there is something inherently wrong w / us, something off-balance & off-kilter from the git-go.
God wants to fix that, but He can't unless we desire for Him to do so. 
Jesus taught that despite God's desire to provide His grace & forgiveness to all, despite the words of the prophets and the Decalogue and Jesus Christ hizzownsef, despite God doing everything He could possibly do to reconcile Himself w / humanity, there were going to be some people who Just Wouldn't Get It.
And therein lies the tragedy.
Logic would say this is not an empty, symbolic, metaphorical teaching; no, Jesus repeated it too often and in the same terminology for that to be the case.
Rather, it is real (or more properly, it represents something real) that is unpleasant and permanent and eternal, something that occurs only by rejecting God.
Indeed, one could say that it is the rejection of God.
Is this to say there is no hope in the afterlife?
Hard to say.
On the one hand, it seems pretty clear that God created us as moral beings, that while we are alive we have that freedom of choice which makes us moral beings. That also implies we lose this freedom of choice when we die, that whatever happens to us after that is immutable.
On the other hand, there are verses about Jesus descending into Hell (Sheol) to rescue those who could be rescued, who would be rescued.
I've posted elsewhere about how God exists outside of Time & Space as we humans understand the concept / s.
Sheol -- that holding cell for human souls prior to the Final Judgment -- may also exist outside of Time & Space.
All the dead "arrive" at the same precise "moment" and all receive their Final Judgment at the same precise "moment", the only difference being that those who opt to follow God depart while those who reject Him stay.
In other words, when Jesus visited Hell / Sheol prior to the Ressurection ("prior" from a human POV), every human who had ever lived was there & waiting for Him, and when He left, He took every soul that would go.
In short, from God & Jesus' perspective, we have already died & been judged (or more precisely, accepted or rejected God's grace & salvation).
We still have, in our limited of-this-world POV, the ability to choose between accepting God's Word or rejecting Him and accepting Hell instead.
And some of us have made that choice and are going to have to live (after-live?) with the consequences of that choice forever.
'Twas ever thus. (Think about it...)
 'Cuz what's the diff between universalism and atheism? Ultimately both philosophies say nothing we do in this life really matters.
 There is speculation that Gehenna is a super-massive black hole that will eventually subsume everything in this Space-Time continuum, which would certainly account for it being eternal fire and darkness simultaneously. I wouldn't bet the heart transplant money on that idea, but it is interesting. [UPDATE: Well, that theory's just been shot to hell.]
 Anyone who has a problem w / that, anyone who wonders why God doesn't just make us behave, ask yourself which is best & most moral: Consensual sex between loving partners who desire a relationship with one another or forcible rape? There's a reason God doesn't force us to behave ourselves & it has nothing to do with any purported inability to do so. So take that, Epicurus.
 This is what John Calvin et al understand as "predestination". Only from our POV, Jack.
(...and a special tip o'the halo to Tatsuya Ishida & his wonderously whacky web comic, Sinfest)