I basically feel that Frontiers almost gets it right. Combat and exploration are generally fun but are held back by certain design flaws. The environments are interesting, but the atmosphere is detracted away from due to framerate issues, rendering quirks, and cookie cutter platforming segments that don't blend well with the rest of the environment. There are a lot of things about Frontiers that irk me, like counters being an easy-win strategy for half the game's enemies, Chaos Island being poorly designed, and certain aspects of the game's control being disjointed and uncomfortable. Additionally the Switch has very noticeable framerate issues in certain spots. It's something of a minor miracle that this game even made it onto the Switch at all.
There are a lot of ways in which the game definitely feels rushed, and it turns what could have been a really fun game into a decently fun game. It's alright, but there are definitely some things about it that I think Breath of the Wild and other open world / -esque titles do better.
What I will say to Frontiers' credit: their boss battles are probably the best to date for multiple reasons, but -- without going into any spoilers -- the major fights nail the pacing and strategy you would want to see from them, and they are unquestionably stylish. It also needs to be stressed that the soundtrack is phenomenal, and the storyline is honestly rock solid. Frontiers succeeds in its more serious tone where titles like '06 failed, and I'd argue most of this comes from Flynn's ability to juxtapose the more cartoony elements of the Sonic franchise's characters with the game's central themes of loneliness, isolation, etc. It also helps that the dialogue and English VO performances were also well done, which is praise I can not give to Breath of the Wild.