I just finished watching the last of the Transformers cartoons (all of the first series) and I think that I can easily say that the show started good, got better and better, peaked after Season 2 with Transformers: The Movie and then went downhill slowly through Season 3 and ending in mediocrity with the Rebirth mini-series (aka. Season 4). Seasons 3 and 4 suffered from an excess of commercialization in that the show seemed to be pushing half a dozen new toys every few episodes. The same commercialization could be seen in the first 2 seasons but was done with more subtlety and background.
My complaints about Seasons 3 and 4 aside, I still found the overall experience quite enjoyable and recommend it for the die hard fans. Watching it in full instead of random episodes here and there when I was too young to keep them stored in my head gives a fantastic perspective on the whole storyline and the characters themselves. Of course, the full perspective also gives me a real appreciation for the shear quantity of gaping holes in the storyline and crazy faux technical lingo. It makes me wonder if it wouldn't be possible to convince someone to fund a complete remake of the original series; rewrite all of the old stories, cut a few, add a few, create overall continuity and then outsource the animation to some Korean studio that'll get whipped by some guy until bear drives in and Tom Cruise saves the day.