I recently resigned from MARS due to an impending move to an HOA-dominated area. (It's hard to meet on-air participation requirements if you don't have antennas of your own!)
MARS has and continues to evolve. While there is still a very little bit of morale activity (there are still some deployed troops that don't have civilian phone access; plus most of the Armed Forces Day stations are run by MARS), the bulk of the organization is now focused on training to help the federal government collect and relay information in the event of a communications outage.
There are a lot of sharp operators within MARS, and there's room for more folks who want to help with that kind of work and are willing to put in the time and effort to train.
The minimum participation requirements are for 12 hours on HF per quarter...but there is a lot of poking and prodding to do more than the minimum, because there is quite a bit to practice on.
One thing that will drive some potential MARS members nuts is the increasing focus on security. Depending on the region, almost all or all traffic is encrypted now. So much MARS information is FOUO that it can be a little challenging to talk about it.
Probably the most challenging elements of the MARS program for civilians these days are:
1. There are procedures for everything. While the rules have been tweaked to tolerate minor deviations, some hams may struggle with the notion that "this is the way something should be done/said", period, full stop. (But once you get over that hump...everyone being on the same page procedure-wise makes things run much, much better in adverse conditions.)
2. Information flows up and down via the chain of command. Only information that you need to know flows down. It can be rough for folks who like to be "in the know" to accept that sometimes you won't have the big picture. That's just the nature of the sponsoring organizations and the agencies that make use of MARS' services. (And it may explain why it's difficult to get good information on MARS from outside the program.)
3. While there are MARS members who will bend over backwards to help get new members operational, even with that assistance, being an effective MARS operator requires a certain ability to be self-starting. Someone who needs a lot of hand-holding might find the experience frustrating..
4. The published minimum participation requirement really is just a minimum; you need to participate more frequently, and regularly if you're going to be effective. If you're considering joining, try to find out when your state/regional nets are, and consider whether you will be able to join them on a somewhat regular basis. I still work; when I originally signed up for Navy MARS, I chose that service because the nets fit with my schedule. When it came time to transition away due to the program going QRT, I struggled because the Army and Air Force MARS nets were held at times that didn't fit in well with work and family time.
I enjoyed my time in the program, and will probably rejoin if and when my circumstances change. There are a lot of good people in the program, there are plenty of opportunities to learn, and the program has turned the corner to having an actual mission again (and an opportunity for folks to make useful contributions for)...even if security/paranoia concerns mean that some details of that mission aren't always known.
Oh, and because the folks involved with processing new member paperwork can get very busy with other tasks...while submitting an online application from an Army or Air Force MARS website will start the paperwork moving, it might be more effective to make contact with a current member, or to corner someone at a regional hamfest where MARS might have a table, to get your membership paperwork shepherded along. Random email contacts aren't as effective (in MARS or otherwise) as they once were.