Windows in a house may not at first make a huge impression, and usually it's not the windows themselves, but the light they bring in, or the views that they allow of the outside, that really makes the impact.
However, when one really starts living in a place and actually looking at using the windows day in and day out, little things start to have an impact. In my case it was the little things, like the off-white color, the small chips in the sill piece, and even not so little things, like the ripped screens that didn't go up and down properly, broken mechanisms and handles, and yes, even a pane that would only stay in if the window was locked, started to add up until I decided that now, in the midst of my full renovation, was the time to replace the windows. I was in a way fortunate that I do not live a block to the west, which would place the house in a historic district and require the installation of wood windows. Not that I don't think that the house doesn't deserve wood windows, but I didn't believe that my budget would have allowed them, given that wood windows can cost three times as much as vinyl replacement windows. I opted to use Window World -- my parent's and sister having recently used them to replace the windows in their own homes and highly recommending them. I ended up taking the advice of my brother-in-law and ordered the Comfort World 4000 series with argon gas option for energy efficiency. With this, the windows meet the Energy Star rating for energy efficiency. The installers arrived at 10 am and worked until 6 pm, which actually was a longer period of time for my mere 6 windows than for my families houses with many more windows, but I also had a smaller crew (two installers) who had to reframe the two rear windows and replace the wood exterior jambs on three other windows that were rotted. The rear bedroom windows were reframed to level out the heights of the windows, which were at different sill heights as a result of the window and door opening (below on the first floor) having been torn out and replaced at some time for some unknown reason. The end result is much better than what I started with. I'm very happy with the look and operation of the new windows. I'm actually now somewhat reluctant to cover them up with bars, so I'm opting to just reinstall the rear window bar on the kitchen window. Thanks to a lot of street presence and a front porch neighborhood, I feel confident about keeping my unobstructed views to the street as well. So it seems even my views have benefited from these new windows.