Is marriage a good thing?

Yes, it is good to be married.

God said wasn't good for Adam to be alone, so he created the animals, hoping that Adam would find a help meet (spouse) among them. When none satisfied Adam, God went to Plan B, by making a woman (Eve) out of Adam's rib.

And the Lord God said, It is not good that the man should be alone; I will make him an help meet for him. And out of the ground the Lord God formed every beast of the field, and every fowl of the air; and brought them unto Adam ... but for Adam there was not found an help meet for him.
And the Lord God caused a deep sleep to fall upon Adam, and he slept: and he took one of his ribs, and closed up the flesh instead thereof; And the rib, which the Lord God had taken from man, made he a woman, and brought her unto the man.

And Adam said, This is now bone of my bones, and flesh of my flesh: she shall be called Woman, because she was taken out of Man. Therefore shall a man leave his father and his mother, and shall cleave unto his wife: and they shall be one flesh. Genesis 2:18-24

In a possible endorsement of marriage, Jesus quoted the above passage from Genesis. [But see what he said later in the same chapter (Matthew 19:10-12, quoted below), saying that it is better not to marry.]

For this cause shall a man leave father and mother and shall cleave unto his wife. Matthew 19:5

There are a few other verses in the Bible that speak well of marriage.

Whoso findeth a wife findeth a good thing, and obtaineth favour of the Lord. Proverbs 18:22
Live joyfully with the wife whom thou lovest. Ecclesiastes 9:9

Marriage is honorable in all. Hebrews 13:4

First Timothy says that a bishop must be a blameless "husband of one wife." So it must be OK to marry. Although if you're a bishop you can only have one wife. (Non-bishops presumably may have more than one wife.)

If any be blameless, the husband of one wife ... For a bishop must be blameless. Titus 1:6-7

And when the world is about to end, seducing spirits and devilish doctrines will forbid people to marry.

In the latter times some shall depart from the faith, giving heed to seducing spirits, and doctrines of devils ... Forbidding to marry. 1 Timothy 4:1-3

No, it's better not to marry.

Paul thought it was better for Christians not to marry.

It is good for a man not to touch a woman. 1 Corinthians 7:1
For I would that all men were even as I myself [unmarried]. ... It is good for them if they abide even as I. 1 Corinthians 7:7

And so did Jesus, who said that those who are worthy of heaven don't marry.

The children of this world marry, and are given in marriage: But they which shall be accounted worthy to obtain that world, and the resurrection from the dead, neither marry, nor are given in marriage. Luke 20:34-35

And when his disciples said that if divorce is not an option it is better not to marry, Jesus agreed, saying:

All men cannot receive this saying, save they to whom it is given. For there are some eunuchs, which were so born from their mother's womb: and there are some eunuchs, which were made eunuchs of men: and there be eunuchs, which have made themselves eunuchs for the kingdom of heaven's sake. He that is able to receive it, let him receive it. Matthew 19:10-12