How should a Christian object to those who say Paradise may be a little boring? From time to time while reading fiction or poetry or whatever I stumble on a certain kind of, so to say, 'satire' of the Paradise the main point of which is that the everlasting live would be meaningless and boring.
For example 

a) we would pursue the same pleasures again and again and this would lead to a comic effect. (see Julian Barnes 'The History of the World in 9 1/2 Chapters')

b) other people in Paradise may tend to alienate a certain person, as well, as angels may tend to look down upon ordinary people and thus suffering would not end. (See Tiger Lillies  'Heaven to Hell' song from 'Brothel to the Cemetary' album)

c) We can be separated with our closest relatives as they can be sent to Hell instead (see Mark Twain 'Captain Stormfield's Visit to Heaven')

How do I object?
If we could envision exactly what Heaven is going to be like, it wouldn't be Heaven, just as if we could comprehend God, He wouldn't be God.  

Just as man should not create (in their own minds) a God made in their image, but understand that man was made in God's image.  So too we must not make Heaven in the image of the earth, but understand that earth reflects in part the image of Heaven.

When we think of playing a harp on a cloud in heaven and singing for eternity, I admit that it doesn't really sound like heaven--even though I love to sing and I think harps are really awesome.

Let me address your three points:

a) experience the same pleasures over and over again:  This is an earthly perspective.  There is no indication that we will be bound to pleasures that will lose their impact and result in boredom.  Rather, God being God certainly would have the capacity to give us eternal joy.  In fact, if God is infinite, it will take an eternity to get to know Him fully.

b) Looking down on others in Heaven:  Angels certainly have a special place in Heaven, having never known sin.  However, we have a special place as well, for we are the only ones for whom God the Son died.  God never became an angel, but He did become a man.  God's glory will be sufficiently wonderful to drown out all sin.  There will be no jealousy as we will all be overflowing with joy.

c) Separation from people we love:  Wherever you go in the world, it becomes evident that we were created for relationships.  However, we were not ultimately created for relationships just with each other, but for the ultimate relationship with the Ultimate Being.  So, our relationships with others are only shadows of the greater relationship we will experience.  Our joy of union with God will be far greater than all other unions.  

God created us for Himself, and He will not merely satisfy us, but will give us abundant joy for eternity.  God is infinitely able to do immeasurably more than we ask or imagine.