These are my own personal thoughts.
Part I: Ravnica at War - Momir
Out of all of the parts so far, I feel that Momir was the most fair. Not necessarily the least annoying but I felt it was the most fair in terms of deck construction (or lack thereof). Once you figure out the mathematics behind what card(s) are likely to be cast at each CMC, the game becomes far more enjoyable to play. I'll concede that not everyone liked the sheer randomness involved with Mommir. I genuinely felt sad for my opponent who kept casting for 9 CMC and getting only Zacama, Primal Calamity into play every time. It took me a little while to figure out how things really worked. Once I reached the final goal and got my dailies I just kept conceding every round afterwards to boost other players. I tried to play until my opponent or I went down to about 10 life then conceding to give them their other dailies but too many conceded before that happened.
Part II: No Escape - Pauper
Until this came out on Arena, I never really played Pauper. Apparently, I tried a Magic Format that used only commons and uncommons (peasant I think?) but I wasn't much of a fan of it so I figured pauper was just more of the same. I confess I actually like this format and might build a proper pauper deck. There are some pretty surprisingly powerful cards in the format. I eventually settled on nice WB with Ill-Gotten Inheritance and Epicure of Blood as the jewels.
Part III: Storm the Citadel - Singleton
I thought this format was the most annoying until week 5. All because of two cards, Rat Colony and Persistent Petitioners. Those decks are just outright annoying (sorry fans). When I built my singleton, I gambled that a lot of people would play these two decks and built a WB deck with every single removal spell I could shove in there. Then I did a rare thing and pushed the deck size to 75. The gamble paid off when the first game was against Petitioners. Despite milling every chance he got, my removal eventually exhausted his deck and he conceded. That's what most of the Colony or Petitioners players did, concede when too many of their key cards were removed. I estimate about one out of three opponents I faced off against was playing one of these decks. I find these two cards against the spirit of the format and annoying to play against. Every other deck I played against was actually an enjoyable experience.
Part IV: Commence the Endgame - Counters
This format is just... borderline awful. Nearly every game just dragged for at least 30-40 minutes because each player was always guaranteed at least one creature at every turn, always. One opponent had a 60/60 zombie on the field but wouldn't do anything with it. It was just constant chump blocking back and forth or just sitting there and seeing who can accrue a larger army. I finally settled on a WG deck with reasonable board wipes, land ramp, counter ramp and evasion.
Part V: Gideons Sacrifice - Ravnica
I didn't want to play this one though becauseI have a limited Ravnica block Arena collection to build from. I experimented with several iterations of a WB, WRB, and UG with really low win rate until I finally settled on a WR deck that was somewhat playable. I eventually eeked out enough wins but it was not an enjoyable experience. This format felt too much like a chore. Thanks for all the fish Wizards. At least my most satisfying win was against a Petitioners deck that managed to get 4 Petitioners on the field. Opponent milled me down to 26 cards and he was down to 5 life when I top-decked Inescapable Blaze. The most hilarious was when someone thought it was a good idea to play
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