OK if you're used to mobile games like Clash of Clans which is of course, fun, purposeful and highly involving, then Miitomo will be on the other end - boring, random and nothing much to do. Otherwise it's an OK start for Nintendo's first go at mobile "gaming" if you could even call it that.
The trouble with Miitomo is that there's really not much variety to do - you basically "buy" different clothes for your Mii and you answer random questions and write random questions for others to answer. Of course, you can customise your Mii, but really there's only so much you can customise. It's not exactly a Skyrim-level customisation - it's rather basic. Within the app itself, there isn’t even any mini-games you can play, so all you see is this Mii of yours that walks round and round in a claustrophobic flat or apartment.
The other bugbear I have is, for what little it is, it certainly takes a long time to load on mobile. Maybe I'm spoilt by the quickness of Clash of Clans to load.
I haven't written this off, but Nintendo will need to make get players more involved with more content and purpose before I feel satisfied with Miitomo. OK first effort but hard to recommend at this stage.