What do you consider the most impressive debut games for a new IP, and what about them specifically makes them the best in your view?

Half-Life 1 if we're talking IPs that have since grown into series. Lightyears ahead of its time.

Nine Hours, Nine Persons, Nine Doors is another great one.

Arms was probably the most innovative new ip. Its crazy how the arms stretched

Splatoon, a fresh unique take on a shooter thats actually very fun and addictive.

The Legend of Dragoon

It's the best game ever.

If the game had to become a series:

God of War

The Legend of Zelda. It was an absolutely amazing game and Nintendo made sure we knew it.

You're talking about the quality of the first entry of the franchise compared to the rest of the franchise or the impact this game had on the game market? If it is the second option I would go with Pokémon, hands down. Red/Blue's impact is legendary, everybody knows about Pokémania and Pokémon now is biggest franchise of all time to this day

Just the quality of the original game, not necessarily compared to those that followed or its impact.

Demon's Souls

Well technically the franchise started on Dark Souls, but Dark Souls is kinda of an spiritual successor to Demon Souls

Regardless which one you choose as the start of the franchise, they are arguably the most important and most influential game released in the last ~20 years or so

This thread could probably end up being a pretty comprehensive list of major IPs, so I'll skip most of them. Instead, I'll focus on one: Ghost of Tsushima. It was a lot of fun when it was released. I recently got a PS5 and Ghost of Yotei, and... it's great, but not having played Ghost of Tsushima in a while, I'm not sure they actually improved much, nor was actually much to improve. GoT didn't feel like the first entry in a franchise that could become great with more games, it felt like a genuinely great game even on its own. It also feels like genuine fun instead of a jumbled mess of systems, which many games these days are guilty of. It definitely has many systems, but they don't feel as disjointed as in many other games.

For some IP debuts that were impressive for their time, Assassin's Creed and Uncharted come to mind. I think they were great debuts... but they also felt very much flawed, where their sequels do so much to improve, and improve they certainly did. But Ghost of Tsushima had none of that, it was great from the start. I guess it's also remarkable to stand out despite the flaws the way Assassin's Creed and Uncharted did, however - not many games manage to stand out like that with such flaws.