The first thing you'll notice about any Monogatari episode isn't the characters or mystery aspect, though. It's the weird visuals and rapid-fire shifts in perspective. For instance, when Araragi arrives at school, you may see a bike ride passing huge streams of cars and/or people followed by a screen full of infinite-length bike racks. Or when a couple of characters are walking up some stairs, the screen may have a huge spiral staircase, or look like an MC Escher painting. The perspective will shift at odd intervals, and occasionally flash to a mostly blank screen with a bit of text (usually to denote a character's thoughts). It's a very strange visual style, and requires paying close attention to have an idea of what's actually going on.
Then there are the long (and often rambling) conversations between characters. It's not uncommon for most of an episode to be just two or three characters sitting around someplace, talking back and forth. The conversation usually has something to do with whatever mysterious occult thing is going on, but often it takes a good long time for them to get around to the point. Three or four such conversations might make up an entire episode. Action is a pretty rare thing. When it does happen, often you don't actually see it but rather hear a description through conversation.
On top of that, Monogatari has a harem aspect to it. Araragi is always surrounded by girls, and usually some kind of crude sexual reference jokes make an appearance. Occasionally even with his younger sisters or their friends. It's never directly abusive or pornographic, but there's no doubt what the writers are getting at. They often turn it around to poke fun at Araragi, and by extension all the otaku perverts out there, but I think they could have skipped that stuff entirely and been better off.
So with all the weirdness and lack of action and harem stuff, why watch Monogatari? It's strange, no doubt about that. Nevertheless, I find the process of understanding whatever occult thing is going on to be highly entertaining. I'm almost always surprised by some kind of twist in each story. There are quite a few recurring characters that develop a good amount of depth, largely as a result of those long and rambling conversations. And as for the harem stuff, well, learning to ignore that is pretty much a prerequisite of watching any significant amount of anime.
There appears to be no lack of material for more Monogatari. There are several series out already, the most recent of which is Owarimonogatari, which I'm halfway through. And there's a film series being developed, the first part of which was recently released (though I've not yet tracked it down). I expect to spend some more time in the future puzzling through the weirdness of Araragi's life.
