Correct. It is just another difference between consoles. Though it does look good for not only a 1999 game, though probably the best-looking PSOne game I've ever seen.
The PSO Rayman 2 version was a real challenge. The game is a bit shorter than the N64 version but it was a great game for PSO anyway. It was developed by UbiSoft China from the main Rayman 2 version, I think.
If Ubisoft (Even if it was the Shanghai studio, well done still.) can make a nice looking volcano like that in Rayman 2: The Great Escape, I wouldn't mind another volcano.
Welcome to Pirate-Community! I don't think it will be one huge level, though huge levels is what I'm guessing. It will be less linear than Rayman 3: Hoodlum Havoc, though, it's still a platformer after all. Once more, enjoy your stay!