I have this book, and I like it(though these is not my first endgame book). For those who have tried it, would you recommend it to other as his/her first endgame book?

I like silmans complete endgame as published in the e+chess app the most

Silman's book but don't pay attention to the separation of information by rating.  Silman's explanatory prose is probably the best you will find but I chose to read by category instead of rating.  Nunn's book is great and the two compliment each other well!  VERY well!

AND, to be quite honest you may even want to check out Silman's endgames courses here on Chess Mentor!  They are superb!  And better than any endgame book I have ever seen. 

Check out these two Chess Mentor courses both by Silman:

Ending, Openings and a taste of the middle (a detailed course on king and pawn endings)

AND

Rook and other endgames.

These two course are amazing.

AND for a first endgame book don't overlook Pandolfini's Endgame Course as a supplement.  Think of Pandolfini's book as a workbook as oppossed to an instructional book.