Personally, the Bartimaeus Trilogy had one of my favorite series endings.
I find it exceedingly difficult to stomach butterflies-and-rainbows resolutions. They simply make the story feel false and sugarcoated, unlike the realism of this trilogy.
I felt that the Bartimaeus Trilogy was very, very cleverly written- not only Bartimaeus' little witty quips, but also in the sense of plot and character development. The way that Mr.Stroud showed said development was interesting as well, such as using Nathaniel's alias in Ptolemy's Gate and finally switching back to his birth name when Nathaniel stripped off the masks that he had layered on his true self.
His death was tragic, but realistic. I cannot imagine the Bartimaeus Trilogy without it.
Despite that, I still have not forgiven my brother for spoiling the ending for me.
Signatures are for triangles.