The MCAT is definitely harder than the GRE.
Getting a top 25% score is not terribly difficult... its easier in my opinion to get a top 25 percentile GRE over a top 25 percent MCAT.
Most MD/PHD programs dont require it, I know of only a few who recommend it and only one that absolutely requires it (Michigan BME).
The quantitative (math) section was very easy in my opinion.. it only goes up to trig, and doesnt even cover calculus at all. Seems too weak to me from a college graduate vantage point, but oh well.
The verbal (analogies, synonyms, antonyms) was the hardest because they put words on the test that you never see in daily conversation. They use all kinds of obtuse, rare words that you would only find in 18th century English literature. The reading comprehension section were fairly easy, I just hated the stupid analogy section. I thought they were going to remove that section from the test, but I dont know if they've done it yet or not.
The analytical was the funnest section to me. It has logic puzzles and games to figure out. Some of them are easy and only take a minute to crack, and some of them will have you stumped for 20 minutes or so trying to figure out the key relationships to solve the puzzle. I spent the most time preparing for this section. Once you get some practice in thinking about the most efficient way to analyze the puzzles, you can quickly ramp up your speed on this section.
For MD/PHD, the analytical/quantitative are far more important and relevant than the verbal section. I'd say that as long as you can consistently get above a 600 on verbal on practice tests, that you should just focus on the other sections.
