Observations from my son's year at one of the top JUCO programs
Good:
Tons of exposure to D1 and MLB. Lots of eyes in the stands at almost every game. Some programs have excellent relationships with Scouts, head coaches, and summer leagues.
Cost of attendance was near zero AND he could take as many classes as wanted. If you have a general idea of a major, and an idea of what type of school you would like to land at, you can work with an academic adviser to make sure you are taking the correct classes. I believe all of my son's 36 credits transferred to his current school.
Quality of play is very strong. Son's team had 11 players move on to MLB or D1.
Academic workload was not particularly hard.
Bad/Ugly
As has been mentioned, no rules on practice frequency and length. It can be a real grind. I believe my son's team practiced 97 of 99 days in the fall. A couple days each week they had 2 full practices!
Lots of quality players for sure, but everyone on the roster has a different agenda (MLB, D1 transfer, some just want to play another year of baseball) Not your traditional "band of brothers" scenario that some may be seeking.
Lots of long bus trips, with some sketchy accommodations. Son didn't seem to mind, but the travel can definitely take its toll.
In summary, my son's JUCO experience was pretty much exactly what he was told it would be. Some good, some bad, but ultimately it yielded the desired results.