Holy f5ck. I am nervous now. Um....after reading this forum I don't think I want to do the HPSP. I feel like I am going through this process blindly. I just want to weigh all my options before school.
There really isn't any reason to not have all the info you need to make a good decision. There is plenty on this site, but realize that by it's very nature, the information will be slanted against military medicine. The reality is that the more disgruntled you are, the more energy you have to spend on a medical student website forum. Now that being said, most of the disgruntled posters have valid experiences/points but I would argue that these experiences are not the norm. Others will vehemently disagree with me on this.
The key things you need to understand are.
1. Each service is dramatically different, and many preconceptions people have, i.e. that the AF is more civil or "cushy" are often wrong. In a paradox the Army is much less hung up on rank and title than the Navy or AF. Each service has positives and negatives. You just need to figure out which gels with your goals.
2. There is no free lunch - The military is going to pay for school, give you a signing bonus and pay you a stipend. In return, you are expected to pay back through service and by its very nature, you will give up some autonomy. You need to be prepared to deploy at least once for 6-12 months. You need to be prepared to have residency delayed - less frequent in the Army but still happens. That being said, the military is generally not intent on "screwing" anyone but the needs of the service trump the needs of the individual so some people will end up drawing the short straw.
3. Your experience is what you make it. Likeable people who perform well generally get better treatment than lazy or negative people, true in the military and civilian life as well. Deployments can actually be fun (I hesitate to use the word fun here) and a time for growth/personal reflection, and a time to build lifelong relationships and memories. Conversely, they can be a trigger for depression, and bitterness, much of this depends on your outlook at the start and expectations.
4. There is no perfect knowledge - there is no way to be 100% sure any decison is the right one, you have to make your best guess and deal with the outcomes eitherway.
5. Lastly, 4-5 years over the course of a career is actually a drop in the bucket. You will have plenty of time to do whatever you want personally and professionally even if you serve out your time as a GMO and do residency afterwards. While not optimal it isn't the end of the world.
Good luck with whatever you choose.