My playtime clocks at 4:30h and I'm at about 23% completion I think. Just got the fire beam (or whathever is called in english) and I'm about to use it to melt everything I find in the frozen area (forgot its name xD).
So far I'm enjoying Prime 4 A LOT. But there is ONE thing I don't like about it. Once you can ride the bike inside the desert, you can go wherever you want and enter almost every main area in the game. However, the game has a very specific sequence and you must follow this sequence (it tells you to go to Flare Pool next). Because if you decide to visit a different area, you are going to experience a huge waste of time. You CAN enter, say, the frozen area right after you finish Volt Forge. You CAN traverse the entire Sol Valley, enter the different gates of the area and go through their small loading screens... just to find out that you can't do absolutely nothing inside yet. Then you have you waste even more time to get back on track.
I also decided to visit Fury Green before progressing because I didn't know if the game would make me go back on purpouse at some point soon. I wanted to see if I could grab some expansions now that I had the cool psychic boots and deliver the green crystals I gathered so far. So, a trip to Fury Green, then exiting Fury Green. Then a trip to the Flare Pool... and then the game requires you to go back to Fury Green in order to get the flame beam. So even more time wasted.
See, in part this is my fault. In all fairness, the game told me where to go next. And if I had followed the path it marked, I'm sure it would have been very a very fun trip and it would have felt rewarding and great. But the game ALSO allowed me to go to other places. In my opinion, if you allow this kind of (aparent) open structure, you have to allow the player to do something with it. It doesn't need to be like BotW (being able to beat the game in any order you can think of), but there should be some stuff to do in every area you can reach. Specially when there is no fast travel and there are indeed loading times between zones (even if they are short).
In summary: if you are gonna dictate the exact structure and rhythm of the game and I have no choice in it, don't give me the ability to go everywhere. I would be happier if this was a Metroid Fusion/Dread kind of situation where the game locks you on the path to follow. Otherwise, it can potentially waste the player's time and make the game feel like a slog,
Of course, now I will always follow the actual route the game tells me to follow and will only detour once I get a lot of upgrades in order to fully explore previous areas. This is how the game is supposed and has to be played.