I had 9 windows replaced with Window World in Denver/Centennial. The windows where good, however the installation was the worst I ever had for any home improvement project.
The windows where put in crooked, so they wouldn't lock or slide, he drilled holes into the bottom of the window not into the sides to attach them to the frame, the trim finish was all caulk, the installer's knife gut a gash into my new counter top, which he claimed he did not do, installer left broken glass on the outside of my house... it goes on and on. Over the course of a month they sent over another installer to correct the mess the 1st guy made. Eventually the windows operated.
However I am concerned that they are just caulked in and as that dries and weathers, it tends to crack and let in moisture and air.
I guess you get what you pay for. It all comes down to the quality of the installer.
Product or Service Mentioned: Window World Installation.