Turtles Forever oddly brought me a sense of closure to my die-hard fan sensibilities. It was like, as soon as credits rolled, I felt like my era of TMNT was over, and I was able to let go and loosen up for whatever the future held for the franchise.
Soon after was the Nick sale and the PD movies... I would have been a lot less open minded about them had it not been for the sense of closure Turtles Forever gave me. I'll always have my TMNT, which begins with the Mirage Comics and ends with Turtles Forever. Everything after that (the Nick toon, the PD movies, the IDW comics...) I'm pretty lax about "getting it right."
So yeah, I'll always be grateful for Turtles Forever. It was the final chapter I didn't know I wanted