I quite liked the series, but the Third one really let it down.
Here are some of my opinions;
First Movie: Brilliant plotline, and introduced the trilogy perfectly.
Second Movie: Probably the best of the three. When Terminator is the good guy, it remixes the entire interpretation of the trilogy. Truely a wonderful movie.
Third Movie: This really let the series down. It ran off the rails of the series.
But in saying that, the ending was great. (Not when they were locked inside the bunker, I mean when the Female Terminator gets crushed!)