How many episodes to this series are there?

There are 28. I suggest anda to watch it in this order.

The Melancholy of Haruhi Suzumiya I (Season 1)
The Melancholy of Haruhi Suzumiya II (Season 1)
The Melancholy of Haruhi Suzumiya III (Season 1)
The Melancholy of Haruhi Suzumiya IV (Season 1)
The Melancholy of Haruhi Suzumiya V (Season 1)
The Melancholy of Haruhi Suzumiya VI (Season 1)
The Boredom of Haruhi Suzumiya (Season 1)
Bamboo Leaf Rhapsody (Season 2)
Mystérique Sign (Season 1)
Remote Island Syndrome I (Season 1)
Remote Island Syndrome II (Season 1)
Endless Eight (Season 2)
Endless Eight (Season 2)
Endless Eight (Season 2)
Endless Eight (Season 2)
Endless Eight (Season 2)
Endless Eight (Season 2)
Endless Eight (Season 2)
Endless Eight (Season 2)
The Sigh of Haruhi Suzumiya I (Season 2)
The Sigh of Haruhi Suzumiya II (Season 2)
The Sigh of Haruhi Suzumiya III (Season 2)
The Sigh of Haruhi Suzumiya IV (Season 2)
The Sigh of Haruhi Suzumiya V (Season 2)
The Adventures of Mikuru Asahina Episode 00 (Season 1)
Live Alive (Season 1)
The hari of Sagittarius (Season 1)
Someday in the Rain (Season 1)

And don't forget to watch 'The Disappearance of Haruhi Suzumiya' the movie, after anda finish watching series!
:)
Pic: The Disappearance of Haruhi Suzumiya