The general fandom consensus has long been that Turbo's second half was excellent while the first half (including the movie) was poor, but, honestly, I found myself enjoying the first half as much as I remember enjoying the second. The movie, despite some logic holes, is a lot better, story-wise, than perception says it is, and the first half of the season itself has some great episodes in it, like Shift into Turbo, Shadow Rangers, Rally Ranger, The Whole Lie, Bicycle Built for the Blues, Glyph Hanger, Weight and See, The Millennium Message, Cars Attacks, Honey, I Shrunk the Rangers, and Passing the Torch.
Justin is a much better character than he gets credit for being, and his age really isn't the big issue that it's made out to be; he also ends up fitting in with Tommy, Adam, Tanya, and Kat better than perception indicates.