We built a house a few years ago, and no chimneys. Gas boiler and furnace are both direct vent out the side wall, around 8' off the ground. Also have a couple of gas fireplaces which are direct vent as well.
We've only had minor condensation issues with one of the fireplaces (adjacent window will fog up a bit if the wind is right), but otherwise all is fine. I suppose there's a bit of noise outside from the furnace and boiler, but it doesn't seem excessive to me. The neighbours have never complained, anyway.