He [R' Yaakov] used to say, one moment of t'shuva and good deeds in this world is as beautiful as olam haba; the smallest pleasure of a single moment of Olam HaBah is more beautiful that all the lives of this world. - Pirkei Avos 4:22There appears to be an obvious problem here. One moment of each is worth all (or more) of the other? Besides that logic consistency issue, there is also the fact that time is only relevant to this world. What does it mean "a moment" ("sha'ah achas", just so you don't think it's a translation problem) of Olam HaBah mean?
Parshas v'yechi begins with telling us that Yaakov is approaching his last moments on earth, but it uses a funny expression: they days of Yisrael's life convened ("yikr'vu") to die. The Ohr Chaim haKodesh explains that each day/moment of our lives is actually an eternal dimension or our soul. We experience it as a single moment in this world and our actions/thoughts/feeling are what transform it into that "sha'ah achas" of Olam HaBah. If we achieve our potential with that moment, then HaShem stores it away until it is time for us to leave this world. If we do not achieve our potential, then we may get that day back to do better. As long as we are in this world, we can always do t'shuva and improve every single moment of our lives. When it is time to leave, all those bits of our soul come together, coalesce, and leave the body (till the resurrection, of course).
Each moment is then experienced as an eternal dimension of our soul. All interconnected, all vibrant. Each moment is just as poignant and intense as when first experience... there is no dulling of passing time; there's no time to pass. Sounds great, no? So where is the punishment? Olam HaBah just sounds like one big party; and it really is.
Have you ever thought about how the silver medalist feels? The bronze medalist feels great; he made it! The gold medalist feel amazing; he reached the pinnacle of achievement. The silver medalist, though, looks at the gold medalist and knows -- with absolute clarity -- exactly where he lost the race.
I think Olam HaBah feels like that... some moments are gold medal, some are silver. Either way, you are in Olam HaBah and experiencing pleasure beyond what can be imagined in all the lives of those world. Those gold medal moments are the grand achievements, or the moments that contributed to a grand achievement. The silver medal moments are those times that we missed the mark and never did t'shuva. They are forever experienced as "almost there". We understand and agree with the judgement of each and every moment. Not only that, but everyone with whom we have a relationship is there with is (since they contributed to that moment). They are cheering us for our success, to be sure, but at the same time able to see clearly where the defect is. They won't say anything; they won't have to... we'll be are most accurate critic.
The gold medal moments, though, are also experienced to their full extent and intensity. We will cry in happiness at our amazing successes, along with our friends and loved ones. No moment in this world has to be less than a gold medal moment for eternity. It's all in our hands.