Turtles Forever was a very good special, but its treatment of the retro turtles was not a homage so much as a crazy parody. Hopefully this was entirely intentional, because they didn't succeed if they were trying to authentically recall the 1987 series. Now yes, I'm relying on memory and I literally have not seen the original series since the 1990s. However, whatever my nostalgia may do it doesn't lead me to claim that the 1987 series was amazing or equal to the 2003 series. It certainly wasn't, though as 1980s cartoons go it started out very well. For the time, not bad.
From this perspective I say that the series was reliably silly much of the time, especially as it got older. The special's depiction of the retro Turtles' world is pretty much correct, and so is the way it makes fun of the old series' stories and how April literally had to get saved all of the time. But the Turtles themselves, I think, were not absurd.
More to the point, what they certainly weren't in the original series were the semi-cowardly pushovers that Turtles Forever portrayed them as. In the special, they'd fight one moment and get scared out of their wits or utterly stomped in the next. It was incredible how they were literally crying in 4Kids Raphael's arms toward the end. Really? Really?! What *I* remember are the 1987 TMNT charging into goofy fights while shouting "COWABUNGA!" and "Turtles fight with honor!", etc. The retro Turtles in Turtles Forever possessed 10% of that courage at best.
The way it skewered the 1987 villains, however, is pretty much how I remember things. Let's face it, Shredder and Krang became walking pushovers more and more as time passed, ultimately competing with classic Cobra Commander in terms of stunning incompetence. Rocksteady and BeBop, meanwhile, were absolutely their old selves. I thought it was perfect that their idiocy was what did in Utrom Shredder.
Anyhow, count me among those that think that the introduction of the original TMNT from the comics was easily the best moment of the special. The way they took that gritty setting and brought it to life was practically inspired.