***Side door(s)
***Rectangular floor plan, symmetrical at least

I prefer two doors with two small vestibules, but if weight were an issue I would settle for one door. A rectangular floor pattern is a must. My Marmot Swallow is a comfortable 3-4 season tent, but the asymmetrical floor plan drives me nuts when I'm sorting out slightly different length poles and wrestling the rain fly, especially in bad weather and/or low light.
My Sierra Designs Electron may be my all time favorite tent. It weights almost 5.5 pounds, but I don't carry it.