Cell was made up of the cells of the most powerful warriors, so he made sense. I just didn't like how it seemed like a repeat from the Saiyan Saga's fight, but not as interesting. Not that there was anything wrong with that. It made complete sense, because he has that prideful Saiyan DNA, and it makes sense for his to test out his "perfection". I know a lot of people hated his second design and thought it was Toriyama's worst, but I thought it was great! I loved the horror vibe they built up, but when it got to the Cell games, I lost interest in his character. Vegeta and Nappa were way more interesting in the way they would toy with the Z fighters, with the Saibamen. The would just entertain themselves, watching as they murdered them. Then Vegeta sent Nappa to fight them on his own, while he just stood back enjoying the slaughter. He then gave them all a chance to get they're savior, Goku, to help them, while Nappa killed innocents. When Goku returned, they would just stand back and analyze him, and sneered at his "pathetic behavior", as he tended to his friends and son. And well, you guys saw it!
I didn't like how robots created by human scientists were designed to be a threat to Super Saiyans. Frieza was a villain feared by all the supreme gods and even Beerus, the God of Destruction, acknowledged how powerful he was. With just a few percentages of his power, he could casually destroy planets. Goku was able to defeat him. Now, you tell me, any robot on earth could compete with that? I think of that when everyone complains about the "integrity of the Super Saiyan". Even how powerful characters got on earth, nothing could come close to how powerful Frieza was. I really liked their personalities though.
I keep peer pressuring myself to think otherwise, but I still think Boo was a very interesting choice. I thought it was brilliant of Toriyama to design Boo to look so ridiculous, because it's pretty much the worst thing that could happen to people so prideful like Vegeta. That dark carnival-like music that was used for his theme was absolutely disturbing and genius! Props to Bruce Falconer! Being that he was so simplistic, it allowed a lot of interesting character moments for not only the main cast, but random civilians! I love that stuff. It was great seeing a return to that, like in the King Piccolo saga, where criminals were taking advantage of the mayhem and terrorizing others. Although I don't like zombies, it's kind of like that. They're not very interesting characters, but the events that occur because of them are very interesting.