I have a PL-120 and it was my entry-level TT a few years ago. I agree with Big Andy that it is about the best bang for the buck for a brand-new and full-featured entry-level turntable. Overall, mine is OK. I modified it for better anti-skate performance, and in doing so, I discovered that the SL-1200 is built much better. While they look alike, they are really not to be compared - very different animals.
I think there are two fundamental issues that prevent me from making major modifications to this PL-120 turntable toward Hi-Fi bliss. (In other words, I chose to purchase a better Hi-Fi grade set and keep this for utility purposes.) First, I think the isolation is poor - a slight fingernail tap on the table surface (equipment stand, not the turntable itself) is very audible in the speakers or headphones. A sandbox helped, but the plastic body and feet construction just don't make for much isolation. Second, I have issues with the tonearm mass, especially while playing 78s - too heavy and problematic pressings make the tonearm go all woogity when playing, occasionally leading to tracking problems.
In light of all that, I have kept mine and use it as an all-purpose TT. It has every convenient feature you can need (aside from automatic control) and is ROCK SOLID reliable on speed and pitch. It is built well enough that it can be transported around without fear of damage and if it gets a dent or a ding, my heart will not be broken. The internal phono pre-amp is not good (and the wiring is not good, either) but it works.
Don't spend more on a new cartridge than you did on the TT - you might reveal more TT problems in your new sound than improvements in the records!
That said, the AT ML-440, Denon DL-110, Ortofon Red, Shure M97xE, or Sumiko Pearl are all excellent choices and will give very good performance without going too far over $100.
Hope this helps!