JOEL - Jesus said, "In my Father's house are many mansions... I go to prepare a place for you.." (John 14:2) Which mansion we go to depends on who we have become while on earth. We will not go to a mansion that our souls are not prepared for.

"For he who is not able to abide the law of a celestial kingdom cannot abide a celestial glory. And he who cannot abide the law of a terrestrial kingdom cannot abide a terrestrial glory. And he who cannot abide the law of a telestial kingdom cannot abide a telestial glory; therefore he is not meet for a kingdom of glory. Therefore he must abide a kingdom which is not a kingdom of glory." (D&C 88:22-24)

Speaking of the Celestial kingdom President Brigham Young said:
"Some might suppose that it would be a great blessing to be taken and carried directly into heaven and there set down, but in reality that would be no blessing to such persons; they could not reap a full reward, could not enjoy the glory of the kingdom, and could not comprehend and abide the light thereof, but it would be to them a hell intolerable and I suppose would consume them much quicker than would hell fire. It would be no blessing to you to be carried into the celestial kingdom, and obliged to stay therein, unless you were prepared to dwell there." (Discourses of Brigham Young, 95)

Everyone who is saved into any of the three kingdoms will be comfortable existing in the assigned kingdom and will enjoy an existence of far greater comfort and enjoyment than is now experienced by any mortal on this earth.
However, even though the lowest kingdom "surpasses all understanding" (D&C 76:89) those who go there will feel some remorse that they did not merit the highest glory. President Joseph Fielding Smith said:

"Of course, those who enter the telestial kingdom, and those who enter the terrestrial kingdom will have the eternal punishment which will come to them in knowing that they might, if they had kept the commandments of the Lord, have returned to his presence as his sons and his daughters. This will be a torment to them, and in that sense it will be hell." (Answers to Gospel Questions, 2:208-10)

Although for these souls there is no possibility for progression to a higher kingdom (D&C 76:108-112), nevertheless they will be able to grow and learn and progress within these lower kingdoms(D&C 76: 86-88), and perhaps find some happiness and satifaction in that.