Why is eternal life desirable?
Don't get me wrong - I think a "really long" life would be great, but that's not what the Bible is offering.
When I think back to people's "vision of the kingdom" and their ideas about what eternal life might be like (which were nothing more than guesses, let's be honest), it seems pretty clear that people are generally pretty short-sighted on this topic. They speak of creating another universe and being like angels in it. Great, but what about after you've worked on your 300th universe...? what then?
And on what basis do you conclude that you'll even be doing any of those things? The Bible doesn't mention it. In fact the Bible mentions so few details about this apparently valuable prize it is offering, that one begins to suspect that the Bible's writers didn't have a clue about it either. If no one knows what you're supposed to be looking forward to, why look forward to it?
To put it another way, if you're selling a product and yet you don't know any details about the product and cannot adequately describe nor demonstrate it, why would I buy it? Why would anyone but the most gullible buy it?
Is it actually what you want?
Let's explore some issues with the concept of eternal life...
Eternal life actually seems to me to be pretty close to the mainstream Christian version of hell eventually, no matter how you paint it. (Or perhaps it's closer to reincarnation? I'm not really sure...)
For a start, it's full of infinities. For example - given eternity, every possible action could/would be done an infinite number of times. Every pleasure would lose its appeal. Existence would lose its meaning.
Of course, many would claim that we would be "changed" in such a way that experiences wouldn't lose their appeal, or something like that. On the one hand, if we were so changed, it wouldn't be "us". On the other hand, that kind of change sounds rather like making us into simpletons, or giving us amnesia. Speaking of memory - what would you want to remember if you were going to live forever? I suspect we'd be better off with amnesia. That way every day would be full of new experiences. Now it's sounding like reincarnation again.
What does the Bible say?
The Bible goes further than that. It claims that there will be no more pain and no more tears (implying no more sadness). Does that mean you are made to forget any loved ones who didn't make it? Or you stop loving them? Without sadness, happiness may lose meaning too. Basically, you'd have less free will, and your range of emotions would be cut in half.
Once made immortal and incapable of dying, feeling pain, or of sadness, what motivation would there be to do anything any more? What purpose would there be to life? Without death, what is the meaning of life? No need to eat or sleep. No problems to solve. We are told that we would spend an eternity worshipping God. Or else what? We'd have absolutely no reason to worship God, meaning that the only way we would all worship God is if we had no choice. Would you give up free will in order to live forever?
What about identity? You want to live forever? You? Who are you? At best, an eternal "you" would simply be someone else who shared your memories (but not the sad ones right?). You'd need a new body and a new brain for starters. Your experience of life would be different, your outlook different, your desires would be different, your goals different. Who do you want to be for eternity? Is there even an answer to that question?
Sure, I'll concede the fact that I'm using my current experience to rationalise what eternal life might be like, but I've already covered the fact that if the experience is sufficiently different, our identity will change with it.
Besides, no one knows what the Bible is actually offering in detail. You can claim that your faith isn't blind on everything else, but on this - it absolutely is.
Just trust me.
You have to blindly trust that God will give you something you would enjoy (remembering that he could just as easily program you to enjoy it, no matter what "it" is). Also remembering that this is the same God that ordered a man to be stoned to death for picking up sticks on a Saturday (Numbers 15:32-36). Then consider that one of the first things God said to Adam was a lie.
Good luck - it sounds like you'll need it. Let's hope it never runs out ... (pause to let that sink in) ... oh, I guess there is no luck in eternity either. (Since every probable event will happen an infinite number of times, probability becomes meaningless)
Seriously, given the choice of eternal life or eternal death (non-existence), it seems that eternal death is by far the lesser punishment.
Perhaps I'm over-thinking it. Some might say that we don't/can't know what the Bible's eternal life will be like, so this is all irrelevant. But if the Bible is offering something that you can't even imagine, why would you want it?
If you find yourself thinking "You just have to trust God" - well that's what gullibility sounds like.
The Bible is selling you a bridge.