Ok lets examine these claims.
How are the melodies boring? From my perspective, they're pretty catchy imo, they certainly stick in my head. The guitar work, if you analyse it is a lot more than just guitar chords like you suggested, there are lots of cool little melodies thrown in there. Its a lot more creative than a lot of backing guitar work imo, and the solos are pretty neat too. Not sure why you're comparing them to megadeth either, megadeth are thrash, and Dave Mustine is known for having some of the most crazy and intricrite lead and rhythm playing of all time, he's a complete monster, and don't get me started on their bassist Dave Ellefson, who does some completely insane stuff. Its like looking at a painting and going "its not as detailed as Leonardo Da Vinci's work, therefore, it must be worthless"
So... tempo.... The majority of the sonic songs i've heard are around the 160-200 mark? Thats pretty fast honestly. What is your definition of slow exactly? For me, Hotel California is slow. Sweet Home Alabama is slow. Sonic heroes main theme and escape to the city are pretty damn speedy, and open your heart and live and learn are upbeat romps. I'd hardly call sonic music slow, in fact when I think of modern day sonic music, I automatically think of pretty fast, frantic pop rock so I STRONGLY disagree with you there.
Also, you're talking about the quality of music when it is a completely subjective thing. Simple does not mean boring. It might mean boring to YOU but some people like that. Some people find megadeth too fast, too aggressive, with hard to follow arrangements and weird change ups that don't make a lot of sense to them. Some people find that really refreshing. Led Zeppelin are one of the greatest bands of all time - I consider their music boring sometimes. They can make some amazingly intricate and amazing compositions... then some of their songs have 1 bar long riffs that repeat endlessly, but sometimes thats the point - its about mood, its about feel, its not about musical complexity - thats why 4 on the floor beats are so popular in clubs, because it is easy to dance and groove to it. I think thats why Led Zeppelin are so special, they had something for everyone while keeping to a very cohesive and identifiable sound.
I don't want to sound patronising but you need to stop thinking about music as good vs bad and try to understand why someone else might enjoy it. Just because you personally don't like something doesn't make it completely worthless, or "bad".