[Matrixbeast]

02 is a poor follow up. The only character that wasn't just an expy of a previous Adventure character was Ken (Who could be argued that he was similar to Matt's broody phase), and despite that, Ken's character archetype is so overplayed in anime that it doesn't help save things. The Adventure cast is forcefully sidelined via the dark tower bullshit, and the new characters themselves just feel rather flat altogether, even in their instances of individuality. The stories were far weaker during the beginning (Since it's all just chasing and destroying the spires), and while things do eventually pick up, it's kind of a too little too late situation.
The climax was a gigantic let down. Myotismon is revealed to be behind everything out of nowhere, and then he's defeated by happy thoughts. And the ending was too stark of a contrast to Adventure's bittersweet ending of having to abandon their partners.

I just felt 02 was so incredibly poor.

Concerning Frontier, it's decent until the last quarter or so. I swear, that run of episodes just brought down an "Okay" series straight into "Horrid."
Despite it being plot relevant, it felt so much like filler because it's all the same, just with a different backdrop.