Who are your favourite characters in this era, and why?
Thundercracker: The perfect comic foil and a genuine guy even if he chose the 'wrong' side. While he was often shot at, blown up, kicked around and abused as Ransack and Crumplezone's "shuttle" he was still a remarkably valiant combatant, constantly working on his special attacks and even taking down Jetfire in earnest across their series-long "normal-guy rivalry". I say normal-guy as Thundercracker never really recieved a 'real' upgrade unlike many of the core cast.

Scourge: Although he is the 'honourable-bad-guy-turned-good' archetype his character development was very well handled in the show. From a survival-of-the-fittest ruler of Jungle Planet, to the vengeful soul (after being defeated by Optimus Prime), to the realisation that individual strength was not enough (after getting the snot kicked out of him on Giant Planet) and finally joining the fight against Galvatron as the protector of Jungle Planet.

Vector Prime: Yet another Prime but unique. He had a cool design, minicon, sword and served as Optimus' ageless mentor. Although not the greatest combatant and primarily used as a plot mechanism due to his warp capabilities he became a character unto his own with words and presence alone.

Which characters were disappointing or over-used?
Starscream: Although more discreet and cunning than his other incarnations, this Starscream just ended up being mentally deranged in his lust for power and desire to end Megatron. It was kind of creepy.

Soundwave: had 'mysterious motives which simply turned out to be the restoration of their war-planet and the destruction of giant planet

The Humans/Trio of Minicons: I hate to be one of those people but most of the time when they're on screen you're wishing to get back to the real transformer action The story could have been easily written without them.

Thunderblast: She had some great comic moments to begin with but quickly became irrelevant and a walking slap in the face to womens equality.

Who would you have liked to have seen more of in this Series for being under-used?

Metroplex: Appearing so late in the series didn't really help these characters which was really dissapointing as Metroplex was depicted as one of the most power transformers without resorting to combinations/upgrades.

Evac, Crosswise and Override: Didn't really get a lot of decent screentime despite being pretty awesome characters.

Scattorshot: Spent most of the time being the humble tech/communications guy. Even after his super awesome upgrade he was largely confined to data management tasks.

Jetfire: He was Optimus' second-in-command, had the respect of all the other Autobots but never really got to shine. Perhaps he would have been a bigger player in air support if Optimus and Vector Prime could not already fly.