I think the GS review was totally offbase. Are the MK games perfect? No. But no version, especially a portable one, has been. The ones that my friends rave about, the SNES versions which we played to death in the 90's, aren't even close to being this close to the arcade. If anything, I was really impressed by the MK games on the collection, and let down by some of the others.
For instance, Marble Madness, which is one of my favorite games, has been stretched to fit the PSP screen, and it looks really bad. The sound is off on it (too slow), which is something that also plagues Paperboy.
On the plus side, though, Paperboy is actually really good on here aside from that. It's easier than other versions, and a lot of fun. You can also say that about Toobin', an old fave of mine. This is easily the best version of Toobin EVER. IMHO, it even beats the arcade version, because you can just control the guy's movement instead of using the hands buttons. Very nice. You actually rotate the PSP and play it vertically and it looks GREAT.
Some of the lesser known games are a lot of fun here, too. Cyberball, which I never played, is a blast. Ditto Arch Rivals, which kind of makes up for the lack of an NBA Jam on here (no doubt scrapped due to licensing).
In short - there are a ton of great games on here. Some are translated well (MK, Toobin) some are kind of in the middle (Paperboy) and some are bad (sadly, Marble Madness).
If you have any other questions, let me know - I play this thing constantly.
RD