I played it tonight at work and I was pleased with the final product. Hell even the CD artwork is nice. The first load screen is not too bad, then the rest of the game is smooth sailing. Except in Metal Slug X, you still see "NOW LOADING" after you walk through the first pyramid tunnel at the start of stage 2 (just like in the Wii version). Yet it seemed to load faster compared to the Wii version.
I didnt get to play Metal Slug 5 or 6 yet, but something tells me it's pretty much it's similar to the Wii's load time.
Yet I must say, DAMN I love the control setup! Dead-on to what it was like when I played Metal Slug X on PS1.