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Brilliant pets! But I wouldn't have them again - cleaning the cage is a lot of work and you have to put a lot of effort into getting them out and entertaining them daily without them destroying everything. Mine chewed the material holding together the slats on my bed so I regularly fell through when I rolled over in the night and they destroyed some of my clothes. Cats are a lot easier!
I love rats. The only thing that puts me off getting some as pets is that they don't live very long unfortunately. >

I concur. I have a hard enough time with big dogs life spans. >

Maybe at this point I should just get a tortoise. >

Then you have to like someone enough to will it to. >

This. I love rats as pets. Very smart and cute creatures. >

They die young so if you hate loosing a pet that you love, well not a good choice. They are messy. They literally mark their route whit piss when you are letting them out to play. They eat their own shit and sometimes like throwing it around. They can be surprisingly noisy for such small animals. There's simply not as much interaction as with cats or dogs in a way that builds a bond, usually not just due to the behavior but also the short life span. The bond is quite different with dogs or cats that you can build over years with doing things together. With rats both time and actions wise you are more limited most likely. 
I think they are okay but while underrated it's not by much. To many these and other downsides are probably enough. A lot of upsides sure but I'd definitely never get any even if I wasn't allergic. The short life span is a key issue. Ex had some and they were nice enough to keep around even though I'm allergic. My dog loved those little things and was heartbroken when they were out down because of cancer. Kept searching for them for so long after they weren't in their cage. The dog, funny enough, was the rats refuge in new areas after we moved or if something scared the rats when they were out of the cage.