To start, I have an odd craving for bagels now.
Alright. I don't know who can rightly call this unoriginal, because I'm pretty sure I've never played a game where I'm a sandwich fighting a bagel. That's very novel, and I loved the concept right away. The visual aesthetic was clear, I knew what the game expected of me almost straight away (i.e. wait for the bagel to begin panting before I can hit it, as that's the only time he can be hurt), and it was overall enjoyable.
The pattern was a little bland, and the weak spot (simply standing underneath him, jumping to reposition when he jumps) makes the bagel an absolute joke to beat even on Insane. In fact, it's slightly easier to beat the game without taking damage on insane because you aren't locked into a cutscene near the end of the fight (this cost me a hit or two during my first fight with him on normal). That said, I could easily see him being the first boss of a full game featuring this sandwich.
In fact, the whole game felt like a boss fight demo of a game that you should probably be on your way making next. Since I could see this seguing so easily into a finished product, and its production is so clean and the game itself is enjoyable, I give the game 3.5 stars out of 5.