I don't think it's all that hard at all, I passed on my 1st shot last Saturday. I borrowed somebody's ATI study guide but never finish reviewing it and I didn't do any practice tests because I didn't have time. I didn't have a regular spot to take the test, so I waited on standby at 5am in the morning outside the campus building, couldn't sleep at all the night before worrying if I could take the test on standby. By the time I got to take the test, it was 8:30am, my mind and body was completely exhausted, but the time limit on the test kept my brain working. I mean, even under my situation, I can still pass the test. Science part mainly focuses on Bio190 and reasoning, I don't recall seeing any A&P or microbiology stuff (perhaps I was too tired to remember anything LOL). Keep an eye on time when doing Math section, Math weren't tricky or hard either, but you have to be quick. I would suggest answer everything first even you are not sure about the answer, because very likely you will run out of time to go back. If you don't understand one particular topic, say Balancing Chemical Equation, don't stress out, the actual test only has one, at most 2 questions on the same area, they are all multiple choices, you can make educated guess.
I was really worried like you because I read the posts here, but I realize the test is quite straight forward and nothing really in-depth. Keep an eye on time, work fast, read fast, you'll be just fine.