AC Odyssey and levels in open world games
Legend of Zelda: Breath of the Wild doesn't have experience points or levels. There is a progression aspect, where over the course of the game you gain stronger weapons and fight stronger monsters, and you gain more health and stamina by doing all the shrines. But you can (and I did) visit the end content Hyrule castle with a character just out of the tutorial, and with some clever sneaking collect some powerful weapons right of the bat. On the other hand, weapons break, so it isn't because you got those powerful weapons early that the rest of the game will be too easy. The whole thing plays pretty well, with a strong sense that you can go anywhere you want, at any time in the game.
I am currently playing Assassin's Creed: Odyssey, and that is an open world game with levels. Not only that, but the power gain per level is rather steep, and fighting elite opponents a few levels above you can be quite deadly. You definitively *can't* go anywhere you want, at any time in the game. However, there is a system in place which increases the level of the areas you have normally "outleveled". There is always at least a minimal danger everywhere, you are never fighting level 1 opponents with your level 30 character. Even quest of a certain level that you have in your quest log will increase in level when you do.
Frankly, I'm not a huge fan of the system. The linear and non-linear elements of the game just don't mix very well, and it becomes all a bit confusing. With random quests being generated all the time, you never feel as if you "finished" one region, because new quests of your level will pop up again. You always want to take all the quests you find, because some are simply long-term quests, which you might accidentally fulfill while doing something else, e.g. kill 10 Athenian archers, or clear 10 bandit camps. But as a result my quest log is very full, and it is very hard to distinguish between random quests that you do only for the xp, and side quests which unlock other content, e.g. cultist clues. If you go to YouTube and look for videos explaining how to find the cultists of a certain branch, you will frequently be told that you need to do this or that side quest first.
The problem the system causes with the flow of the game is the following: If you only follow the main story, and never do any random quests or side quests, you will get stuck. You will become blocked because your level is too low, or because you didn't do a prerequisite side quest. As you can't "overlevel", the best strategy is thus to do a lot of side quests and random quests, and exceed the level requirements of the main quest. However, that takes a lot of time, and as you can imagine, the random quests also feel very random. As I said in a previous post, sometimes you fight for Sparta against Athens, and sometimes the other way round, possibly switching back and forth several times per day. By the time you come back to the main quest, you have thoroughly lost all sense of purpose.
*Spoiler Alert* The sense of purpose in Assassin's Creed: Odyssey is further complicated by the game being open ended. There are different possible endings, depending how you behave towards the members of your family. You can end up with a happy family reunion, or you can end alone, up having killed half of your family. If you aren't aware of that from a spoiler, you might well end up with an ending you don't really like, just because you were goaded into a conflict.
Compared to Horizon Zero Dawn, Assassin's Creed: Odyssey does a bunch of things better. The ability to climb wherever you want is a huge plus in an open world game. While still far from perfect, the system of crafting and looting weapons in AC Odyssey makes a lot more sense than the one in Horizon Zero Dawn. But the story and sense of purpose in Horizon Zero Dawn is *far* better than in Odyssey. But in the end, I would prefer the level-less Legend of Zelda: Breath of the Wild.