Why was the PSP so good?

Could you elaborate on what makes the PSP, or the PlayStation Portable, so highly regarded? Was it the innovative gameplay, the sleek design, or the impressive graphics that truly set it apart from other handheld gaming consoles of its time? Were there any specific features or games that contributed significantly to its popularity and success? I'm genuinely curious to know what made this device so appealing to gamers and what sets it apart even today.