What’s it like as an Officer in the Army Reserves?

Drill weekends can be very different depending on the assigned unit, there is no one answer to your question. Typically Human Resource Officers are responsible for tracking actions, reviewing awards and evaluations for accuracy, updating personnel records, along with any other group training. In Civil Affairs, the possibilities are a little broader. When I was drilling with CA, we worked on country presentations (doing research and creating a presentation). All reserve Soldiers have to complete mandatory training annually, sometimes it's done at drill and other times it will be on your own. The more you move up the greater the responsibility and the need to invest personal time to keep up.

It can be totally crushing or completely uneventful. You are probably not going to know what you are getting into unless you personally visit the unit during a Battle Assembly weekend prior to signing the dotted line. However, what you see during the weekend doesn’t show you what you might have to deal with during the rest of the month.
As a 1LT I have been crushed. I have been crushed hard. 2.25 years of command time with 160 PAX, and $53M in equipment RFX Quartermaster Company with the last two years of ATs at 28 days and the next two years are slated for NTC.
Examples:
1) Transgender soldier issues
2) Vehicle Accidents both during drill weekends on civilian roads, and military posts
3) Constant admin actions needing my attention for a total 1,800 individually signed actions
4) Training and planning conferences in addition to the actual training event itself.
5) 28 day annual training events (not the 14 days as advertised) on top of the conference
6) Soldiers threatening suicide
7) Soldiers suffering domestic violence
8) Your equipment burning to the ground during a field exercise
9) Your equipment being too tall for a bridge and getting smashed

My experience was hard earned, but now I’m in a non-MTOE unit that is not RFX, and has a CONUS tied METL. That wasn’t without coincidence. Now I can manage my own personal OPTEMPO and focus on promotion required training. I have no annual evals to worry about other than my own. The only thing I’m responsible for now are Lodging Reservations for out of town soldiers during Battle Assembly weekends (which means I have to make sure everyone signs the hotel register).
What I can only recommend is don’t be too eager to take on additional duties or command for which you don’t hold the rank for. The opportunity will always be there, but it’s on you to make sure you use that time to get exposure to what you are getting into before you move into your next position.

yep. It all depends on the unit and current optempo. I've been in units where drill weekend consisted of nothing but sitting around bullshitting for 2 days for months on end and then the same unit where you were running around with your hair on fire. That said, there are always taskers that need to be completed that you just don't have time to do during drill weekend. I typically spend 10-12 hours a month, at a minimum, doing "army" stuff outside of drill.