It depends on what model # it was, since there were NUMEROUS model #'s. The earlier ones some people had Disc Read Errors(DRE) with, while the newer models they released just prior to coming out with the slim PStwos were considered generally better systems.
The two model #'s I consider the better ones were the 39001 and the 50001, which were the last two models before the slim. The 30001's, 30001R's, 33001's and 35001's were generally shitty systems, from what I've seen and I've repaired many of them.
As for the value of the fat models, as probablysober said they're mainly only good for the fact that you can use ummmm non Sony approved software on them. We'll just leave it at that.