Gameinformer had a chat with this Sonictuber about Frontiers. The interview's an hour long, so I'll paraphrase the talk below. Some new info, some old.
- Areas of the map you can't access at first are "fogged over".
- You earn traditional ranks in the Cyberspace levels (S, A etc.)
- Amy only remembers "Sonic is helping me" and "I just want to help the Kocos" at first. Her ability to communicate gets stronger the more of her missions you do.
- Sage SEEMS helpful, but may have ulterior motives. She comes off as "a little stoic".
- Dialogue was limited in the build they played (it was an even earlier version than the one IGN had), but Roger's stuff was great.
- Sonic is alone "for most of the game", but does occasionally talk to himself.
- Quips such as Sonic mentioning that the islands would make a great place for a Chao Garden are there to connect Frontiers to the series timeline.
- Cyberspace seemed to be the driving force of triggering a lot of cutscenes
- Amy's memory tokens (hearts) are marked on your map. Kocos you need to find first are not.
- The place you fish with Big? You have to find Big in Cyberspace first, but once you do, Big and his "fishing place" will also be marked on the map. He THINKS the purple coins you collect are for Big. Elder Kocos that will help upgrade Sonic are marked on the map too.
- You do NOT fish as Big. You fish as Sonic. He also speculates that these "voice diaries" that you can buy from Big's shop are Big documenting his journey.
- Sonic controls "very good". He feels the right weight and connected to the ground. He's fast but "not boost era fast". You'll get to your destination fast though. The only tweaking he thinks was needed was precise platforming with double jumping is "sometimes a little finicky".
- He's not 100% certain about it, but he THINKS there's a battle theme, or a "song that picks up as you enter combat"
- There may be Green Hill in Cyberspace, but there's no remixes of Green Hill's music. It was a completely new song.
- There were TWO levels themed after Green Hill, and one that was Chemical Plant. (Note: Green Hill is the tutorial, so it probably is the reason it gets two)
- He says he thinks he kind of used the "Metropolis" wording rather loosely and doesn't think it's a Metropolis from past games. He also thinks that the city level we saw in the Direct is the one he called "Metropolis".
- He also mentioned a "Sonic Unleashed-themed stage". (Note: This is all but confirmed to be Rooftop Run)
- The tutorial Cyberspace level is very short. He even remembers finishing it in "52 seconds". He says he played only 5 or 6, but he did mention that he thinks that "they were getting longer".
- He mentions that they're not really easy either. He mentions one level, either Chemical Plant or the city one, that took him a few tries. And yes, there's branching paths in "at least a couple of them".
- Some missions in the Cyberspace levels (to get vault keys) involve getting S ranks.
- Enemies that were in the original versions of the levels are carried over to the Cyberspace levels.
- The Chaos Emerald vaults are scattered around the island. For example, you can find one on a hill.
- He feels that there's good momentum as he starts running and stops running.
- We got another re-confirmation, via what Iizuka told him, that we will NOT be seeing a large cast of characters due to the Starfall Islands being an "uncharted place that no one has been to before".
- He says he didn't see more than 7 Cyberspace levels on the island map. However, he was able to play around 5-6 & he didn't even open up all of the island's map. He only played on the northwest part of it. He says he wouldn't be surprised if there was "around 10 on each island".