It's a very different game, not really comparable at all to Elden Ring. It's made by a different team inside of FromSoft and uses the assets of Elden Ring, but plays very differently.
For me I didn't vibe with Nightreign after having spent 1500 hours in Elden Ring. Elden Ring is all about exploration, getting to hard bosses and getting your ass beat for sometimes hours. When the game was new I liked exploring the entire world finding all of the secrets, finding all of the bosses and beating them. When I knew the game inside and out I enjoy doing challenge runs, randomizers, mods etc. Especially doing crazy dumb challenges and getting my ass handed to me, but then overcoming those challenges and getting the feeling of having done so.
Nightreign is very different. It's GO GO GO GO GO all of the time. You need split second decisions about where to go, what to prioritize and you have a ticking clock all of the time. Taking too long to do something means missing out on rewards and perhaps even losing the run. It can be done single player, but it's really focused on having a team. But a team can be hard, if there is someone much better or much worse, the team doesn't work and fails. It's also important to work together, so that usually means just following whatever the one person best at the game does. The order in which you do stuff matters a lot and you need experience to know what works best. The bosses are hard, but when you lose it's just over. You need to do a full run to get back to that boss (and it might not be the same boss, depending).
For me Elden Ring feels like dipping into a relaxing hot bath. Just enjoying the world and even when I get my ass beat by a boss for hours, it's still relaxing to me. Nightreign is the absolute opposite, it feels very stressful especially because of the go go go aspect. I also feel like when I fail I'm letting the team down and it's up to me to do better, but doing better is often more knowledge based than skill based.
In terms of combat, it feels like Nightreign is a bit simpler compared to Elden Ring, but still comparable.