I really liked the first parts of the episode. Basically everything was awesome until Rei showed up. Not that Rei ruined it, but from the point he showed up, everything started feeling really rushed. Revivemon's power didn't really get utilized in any special way (contrast this with Raidramon's or Hackmon's first appearances).
Navimon and Puzzlemon reappearing were probably the best part of the episode. Close second is Mienumon making Musimon and Dokamon attack their friends. It wasn't -dark-, but it did feel -serious-. It would've been the best part of the episode had any of them thought to actually go Super Grade (there's no time limit on that, so why aren't they using that as default in battle?)
I hope to see more of Warudamon, she felt like a fun threat and I love the design for her eyes! I'm surprised we got to see another shadowy Applidriver pull out Sakushimon's chip for the Ultimate fusion. Is it the same one as before with Scopemon?