Despite the limitations, many games pulled off amazing graphics. Many in the thread compare it to the PS2, but that's unfair. Doing better than PS1 graphics in a handheld was quite an accomplishment back then.
Interestingly, the quality of the assets in these games didn't have a chance to show on the 480x272 screen of the PSP. However, many games, including Bloodlines, Gran Turismo, both GTA's, just to name a few, look very close to PS2 when upscaled. So the work was very much put into these titles, and it shows, even after two decades.