The town and class size, as you said, come down to personal preference. I am from a small town, so I really liked it. As far as the class size goes, I expect it to be an adjustment as I currently go to a Big 12 school. That being said, I like the idea of the personal attention I will get and how close the class will become as our time there progresses.
Tahlequah is small, but not tiny. There is a Super Wal-Mart, a Lowe's, a Chile's, and many other local and chain restaurants. Housing is cheap compared to what I am used to. Since you are a resident of Oklahoma (I assume), your tuition will be far lower than if you come from out of state. Additionally, the optometry portion of the college has its own parking, which is a big plus.
Difficulty of getting in - not real sure. I can tell you that NSUOCO only takes students from nine states. The following chart will give you an idea of the scores needed to get in:
http://opted.org/pdf/profiles2008.pdf
Keep in mind that the scores on the above document are averages, meaning that there were students admitted that were both above and below those averages. Since there are only 26 students per class, they are looking for 26 people who they think will get along for four years. Personality and willingness to work with others is important.
As with all optometry schools, they also want you to have some relevant experience in the field. Job shadowing or working for an optometrist is very important and will greatly increase your chances of getting looked at seriously.
I have subscribed to this thread and will be more than happy to answer any more questions that you have. When I was in your position, I also found it difficult to find information on this school. Now that I have seen it and gone through the process, I am more than happy to share!