As a fan of the franchise for several years, following the blue tornado in every success or failure, I have to say that I was surprised (both positively and negatively) by the release of this game. Sonic Frontiers is a pretty decent game. It is far (in many ways) from being a major AAA release (e.g., God Of War, Last Of Us, Zelda, etc.), but there has certainly been an effort to upgrade, which is very evident compared to previous releases like Sonic Forces, Sonic Lost World, and Sonic Colors Ultimate.
A bit more specifically...
Story: Although it started promising, giving you food for thought about what might happen, it ended up making a sudden fast-forward from the first act to the last, leaving gaps and a somewhat controversial ending. The serious tone and the slightly heavier atmosphere is a touch that has been missing from the franchise for the last decade, but for me, it fits perfectly, and I would like it to remain so in future projects.
Open Zone Gameplay: The idea of adapting the small "zones" we are used to in Sonic games into an open-world environment was an idea that no one knew would work in practice. The feeling of moving through the large maps of Starfall Islands, using grind rails, dash panels, bumpers, parkour walls, etc., is truly fantastic and doesn't make you bored in the slightest. Plus, there is always a small incentive to get into this logic, and that is the reward waiting for you at the end of EACH small zone, and no, I don't mean the reward of satisfaction, but a tangible reward that is necessary for the progress of the story.
Ah... And I didn't mention anything about the feel of controlling Sonic... THE BEST control that has ever existed for Sonic in a 3D environment... And because I see the concern in your eyes, YES, it is better than that of the Adventure games... So, fun is guaranteed!
Exploration: When you hear the term "open world," your first thoughts are definitely about the vast areas you can move through, the endless landscapes, and the bizarre buildings you will encounter, the scattered enemies, friendly NPCs, and a ton of collectibles that will be hidden within this gigantic map... Well, in the case of Sonic Frontiers, all of this applies except for the last two. Although we are talking about huge areas where you can run freely and let your eyes be enchanted by the beautiful/bizarre landmarks, you quickly realize that the only thing filling the map is the tolerable amount of enemies and the small zones with grind rails. In a more free translation, it is a variation of the world from Elden Ring, without the collectibles and various NPCs (Well, there is a friend of Sonic on each island, but that's it).
Combat: The combat feels fresher than the previous titles in the series, bringing to the forefront a system where you perform attacks with the press of one or two buttons (Something like the moves from Super Smash Bros). It is certainly not the most interactive combat the franchise has seen (Cough cough, Sonic Unleashed), but it will definitely keep you pleasantly entertained throughout the game. *It may get a bit tiring if you go for a second playthrough*
The Fishing Mini game: Big returns stronger, having learned from his past mistakes, and comes to change the entire mindset of the game because literally, it can break the Game. It is the part of the game that you will love, especially towards the end of the story. I won't say more, you'll understand for yourselves.
Soundtrack: It has EVERYTHING. Lo-fi, Heavy Metal, EDM, House, Dubstep, Pop, Guitar Solos... Clearly one of the top Soundtracks of the Franchise.
After Credits: After you see the Credits, you can definitely return to the Starfall Islands to achieve 100% Completion of the game, but you can also download the FREE DLC "The Final Horizon" which gives you a new story, 3 new Playable Characters, and different Gameplay to enjoy.
These are the "few" things about Sonic Frontiers. A game that certainly started with very Low expectations, and ended up being a decent (not perfect) Sonic Game.. The wait for the next Mainline Sonic Game seems long.