

First level runs flawless, but after 2 or 3 more levels GPU usage hits 100% and runs at 20-30fps. Only a restart fixes this.

Performance is mostly good, but certain particle effects really affect performance dramatically.
Certain particle effects, like the lightning dash and the quick reload on the shotgun seem to affect performance dramatically. On my 3090, the framerate usually hovers around 135+, but when those effects occur, it can dip below 30fps for 2 seconds. It can be very distracting especially since this game is a fast paced rogue-lite shooter.

When VSync is enabled, the frame rate sometimes drops below 60, if there is no limit, then the graph is still not stable, there is clearly an optimization problem. DLSS works well
if the developers fix the existing problems by the release, it will be wonderful, despite how poorly many people optimize games now, here at a decent level

Performance degradation issues, but might be a Demo leak issue.
After about 15 minutes, perfomance degraded significantly. Fix by restarting the game.