I'm usually pretty forgiving of middling plots and willing to give them a chance, but this one is just too generic and weak. He spends seven loops (21 years total) unaware of his "friends"' true nature, and more than that, got killed every time at the age of 18 when entering the same forest. Not against some specific super-strong enemy, but different monsters from the same forest every time because his "friends" would go seek out a strong monster to watch him struggle against it for their amusement. Like clockwork, every loop after three years apparently.
It's such a weak backstory, and just makes him come across as genuinely stupid. The fact he apparently never thought to mention the loops to them ("Hey guys, let's NOT go into that forest today, I have a bad feeling"), or never found it odd he'd die against different monsters in the same forest. Seriously, I just can't get over the fact it was always the same place apparently. You'd think there'd be some variety as a result of his choices in every loop, but apparently he just trained new skills for the next time they'd go to the forest.
Not to mention everyone so far is just... generic. Snobby nobles to get revenge on, a princess who's looking for talented people and is just teaching him skill after skill so he can show up the snobs, and the protagonist is especially generic. And then he gets OP powers because he'd train a new skill (for three years) in every loop (which last three years), which apparently accumulates/carries over once he gets past a mental block about his skills resetting (to instead unleash three years of experience).
Yeah, no. He should NOT be that strong from just three years of training a skill. The fact he never noticed until the princess pointed out kinda shows he never tried to train it again because even if he DID physically start over from scratch every time, he'd still have the knowledge. Still remember three years' worth of stances for sword fighting or magic incantations, so he'd have a more solid foundation to use for training and quickly advance. Which SHOULD have let him notice the accumulation more quickly.
Overall, just a very disappointing manga only four chapters in. Fastest I've found myself totally disillusioned with a protagonist.