Water
Access
Neighbors
topography
nearness to town
Water - if you don't have water you're not even up s___ creek, you're up a dry river bed. Water is the beginning of life. You can get by with less, create storage systems, swales, etc, but you're pretty much stuck with the water that either falls on your land or you can get (using energy from somewhere) from a well. If you're dream is to get by on 6 inches of rain a year, embrace it, but realize what you're getting into.
Access - This will vary with the individual. Some folks may want a home you have to back pack in 20 miles to reach, or even fly into. I want something I can get a vehicle to. I had a friend who would had a long clay driveway that would turn into a mud hole every time it rained. He routinely had to leave his four wheel drive stuck until it dried out in a few days. (That would be include, access to various parts of the property. Once again, look at what you want/need to fulfill your dreams.
Neighbors - I don't mind someone a little 'careless' about their property, but I have an aversion to drug addicts, thieves, etc. If you're pretty 'straight' you might not even recognize the signs. I lived next to a meth addict for a few years and I was too damned green to recognize what he was. A couple of guys with more 'street knowledge' came by the house, at different times and without knowing the others assessment, saw my neighbor from the end of a long driveway and said "Oh, you've got a meth head living next door". When I moved, he broke in and robbed me of most of
my stuff (I was coming back for it). Everyone has their preferences for who they live around (some folks might be fine with a meth head but not want to be around 'church people'. Figure out what you want and what you won't put up with.
Topography - I'm at an age where I have no desire to go mountain climbing to walk to the back of my property. Varied Topography can be a blessing (water power) or a curse (erosion, places you just won't go as often as you
should). Weather conditions can emphasize problems with topography.
Nearness to town - Again, it varies. Some folks are like Pecos Bill's dad. Someone settles 20 miles away and they think "the country's filling up!" Personally, while I treasure my wild spaces and want plenty of 'elbow room', I also don't want to drive 2 hours round trip for a bottle of aspirin. I'm good with a 1/2 hour from town. Nearness to town also translates to nearness many resources that are there, as well as alternate or emergency employment opportunities.
Power - maybe this isn't a priority for you, but having commercial power is sure nice.
Internet access - may not be a priority for you, but once again, it sure is nice.
Make sure you are on the same page as your spouse. My wife has even tighter 'near to town requirements'. She is fine with my ideal of 20 acres of wilderness, as long as it's on a good road, with nice neighbors, 5 minutes of less from all her shopping needs, preferably near a major university. We laugh about it (I may have exaggerated her list a tiny bit). Realistically, we are still working together to figure out which of those requirements is going to be adjusted, because unless some unknown billionare uncle dies and leaves me a huge pile of cash, there is no way all our wants are going to be met.