I've been to Cancun around 45 times, been going since 1990, what do you want to know? Great people, I definitely noticed the bars are less populated than in the past but you are going in March should be good, I hope you are college aged. I went with my wife once in March, I was 32 yo and felt like grandpa, I couldn't deal with the douche bags.
Do not rent a car, you will get pulled over and they will fine you (they always do) and lately there has been a lot of publicity on drug killings (in Cancun) and bad alcohol at some resorts where Americans have died. I was there in October and my hotel served beer in cans/bottles so you could protect your drink.