I was offered an appointment to participate in OCS at Pensicola in 2000. From there, I would've gone onto the Naval Intel program in Virginia, then, from there to Monterray, CA. I took all of the tests and passed with flying colors. Ultimately, I turned it down. That being said, I learned that OCS was 12 weeks of very demanding training and re-education to put you in line with the Navy way of thinking. Realize that OCS involves Marine Core drill instructors on your case for 24/7. They don't care who you are; you belong to them for those 12 weeks.
My advice if you decide to do it...
Get in shape NOW. Run 5 miles a day, 5 days a week.
Teach your body to get used to 6 hours of sleep a night. Go to bed at 10pm and get up at 4:00am.
Get used to taking orders from people that MAY not be as smart as you. Get used to hurrying up and waiting, and laziness.
Learn how to swim ASAP if you don't know how.
Start saving money now. They won't pay you much, and the benefits of what you have while in the Navy aren't great.
Your living conditions will be shit, wherever you are (on sea or land). The housing they give you....BOQ - Bachelor's Officers' Quarters...are ghetto. Many officers live off base. Your pay, just out of OCS as a commissioned officer, will be in the mid to upper $20k.
If I think of anything else, I'll edit my post.
Best of luck to you in your decision.