Soundwave is one of the most famous and appreciated of the Transformers characters and is quite a classic. As Botch the Crab notes

There’s so much that’s novel embodied in the concept. A larger robot carrying passengers (subordinates, agents, underlings, companions)! The introduction of sound as a weapon, music as a disguise, communications as a tactical element! I remember the very first time I saw the commercial for Soundwave on television and witnessed him transform from cassette player to robot, open his chest case, withdraw a cassette and throw it at the Autobots, only to see the cassette transform into a robot condor — and it was like a million cool things all collided at once. (Soundwave’s eerily synthetic voice didn’t hurt, either.)

Of course his “vehicle mode” is not a vehicle. As such the “alternate mode is practically defenseless and utterly immobile. Plus, if the G1 Autobots ever took him out before he ejected his minions, the G1 Decepticons would have lost over half their forces.”

I am certain that a lot of the character’s appeal is that he was voiced by Frank Welker, processed/modified, in the classic cartoon. As a toy however he is cool because his play interacts with other, smaller toys. As a toy in his alt-mode he was scaled 1:1, which means that when he was not a robot the toy was the same size as the item he was mimmicking. That is the last time I explain what 1:1 scale is, I hope. There is an irony in that scale, I am certain.

Though Soundwave’s toy is a microcassette recorder, his fictional appearances depict him as a stereo cassette deck or Walkman. (Likewise, his microcassette tapes are depicted as regular audio cassettes.)

Soundwave’s Autobot counterpart, Blaster, transforms from robot to a ghetto-blaster, a boombox. His tapes are the same size as Soundwave’s and they fit into Blaster just right, meaning that his alt-mode is out-of-scale. Of course Transformers toys were never that great on scale in the sense of the robot mode, and the vehicular Transformers were not good on relative scale in either mode. It is just a little odd that of the Transformers that transform into role-playing toys, the two that essentially convert into the counterparts of the other do not keep scale with one another.