Pros
Basically, I got to stay in some of the most scenic places in the country that many people shell out thousand of dollars to see for the price of my labor. But for those who don't just see this as a working holiday, ACE is great for funneling people into long term careers in this field. Since ACE is contracted to work with land management agencies, crew members interested in working for the BLM, Forest service, national parks etc. get basically a week long trial of what people do there. You often working side by side with these agencies' seasonal employees, many who offer to be your contact or reference if you decide to apply for their job. ACE also occasionally invites professionals to come give career talks/ advice to crew members. So for a intro to trail/seasonal outdoor work, gaining the basic skills and all, its great. That + free housing+ (in Utah at least) free food on the off days made the whole thing worth the time imo.
Cons
The pay, but this is obvious. As someone that came in with a number of financial obligations, I left the program with probably the same amount of money as I started minus some % of my student loans. The work itself is extremely variable. Sometimes you get put on a project thats really intense but rewarding and a lot of practical skills are learned. Sometimes you get put on one where the project partner is unorganized, the vibes are off, team moral is low, work is annoying and you just have to deal with it for a week. If you're like me, the pros out weigh these moments.