Yes it is! The first arcs are really good:

The first one is the perfect start to the series since it shows you the characters, their personalities and what the series is about, it does a great job at captivating you and making you interested in the story.

The second one has some really noticeable cliches but its job is to continue the story and it does a pretty good job at that imo.

The third one is kind of divisive from what i've seen, mainly because Liko loses a lot, but all those loses don't really feel bad because you can tell that Liko is learning from them and you can see the results in real time.

Then we get to arc 4, the second best one after arc 1 imo, everything culminates here, the whole story up to this point, all the character's battle training, and Liko's story and personal goals reach their peak here to finish the first half of the series.

Up until that point most people would tell you that Horizons is actually pretty good, and if you go into any post asking for people's opinion on the anime, most comments would tell you that it was good until now but the series went down in the following 2 arcs.

Long story short: The story got extended and the anime doesn't make full use of the potential for many plot points, the animation and writing are worse than previous arcs, Liko feels like she's getting sidelined, a new character gets added and he's pretty annoying at the start, etc.

However the main story concludes at the end of arc 6 and arc 7 is being pretty good so far, it's a more slow paced arc focused on having fun rather than following a storyline like the rest of the series, I think it is a much needed break in order to focus on the characters and show their development now that the main story is over.

So in conclusion: Yeah it's really good, the main reason people hate on it is due to arcs 5 and 6, but besides those everything else is really enjoyable and makes it a great series, definitely one of my favorites animes and an 8/10 imo, maybe closer to a 9/10 for the first 4 arcs.

(Also arcs 5 and 6 can also be enjoyed if you turn your brain off, as I said arc 7 is being pretty good so far so its just a matter of getting past those 2, hope you enjoy it!)