Original Trilogy
The first three TMNT films follow the story line of the original comic as well and featuring the style of humor used in the television series. The second film in the trilogy features the origin story of the Ninja Turtles as it was told in the comic. The films were produced in the 90's and use a live-action style of filming complete with actors in costume and animatronic. These three films were very similar, being produced in the same style within a short period of time. This trilogy probably maintained the same audience through all three films. The second films also includes a cameo by Vanilla Ice (see Music and Video for a peak at this gem). The live action television series of 1997 was shot in a similar style, though much poorer quality.
Fourth Film: TMNT, 2007
This film is supposed to be the final installment in the original series as it picks up where the plot of the third film leaves off. It was produced 14 years after the previous film, however, and was made with computer generation instead of the live action style of the films before it. This films seems to lose the continuity of the other films as it both looks different and was release so long after the others. In the 14 years between releases, the audience for TMNT films would have changed dramatically, as younger fans are introduced and older fans become less interested.
Fifth Film?
There are talks of a new TMNT fifth film that could be release in 2013 or 2014. Though details of the film are unclear, it is rumored that the origin story of the turtles may be changed, with the turtles coming from an alien dimension instead of being mutated by radioactive ooze. The style of the film may return to the gritty, violent style of the comics rather than the lighthearted nature of the previous films and TV series, perhaps in a effort to attract older fans back to the franchise. It will be interesting to see how fans react to these changes.