These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
YMMV: Sonic Rivals
Best Boss Ever: Metal Sonic in the first game's Sky Park Zone Act 2. It's like a 3D remake of the race against him in Sonic CD.
Best Level Ever: Meteor Base from Sonic Rivals 1, by virtue of not having to race a rival at all and just run through the level old-school style.
Complete Monster: Eggman Nega, even moreso than in the Rush games. He plans to release the Ifrit to destroy the world—and to power the Ifrit up, he was going to feed it Chao.
Even Better Sequel: Rivals 2. More playable characters, better level design, better graphics, better soundtrack, and to top it all off, a Free Play mode where you can just run through the level by yourself with no Rival. While this is unlockable, it's a godsend to those who just want a classic Sonic experience with straight platforming and running.
So Okay, It's Average: By and large, those who have played the Rivals games don't see anything particularly bad about the games, but also nothing particularly good that stands out.