I agree with ManiacB:
The first season is fun to watch. Adapted from novels they did a good job to keep the talking heads interesting. This means lots of weird angles, different art styles, live action sequences and usage of colored text cards (appearing for split seconds only). By the time we get to the second season the direction changes for the show. The flashing text cards only appear occasionally and the direction is rather tame. The pace of the arcs slows down and were left with TONS of fanservice (in dialogue and visuals). It is already present in the first season but it's better mixed in so it's bearable. Every female poses like a slut, a loli vampire bathing with the MC and it doesn't stop at his sisters. Much of it also feels like a dating sim: there is hardly any interaction between the girls and they only appear alone in scenes with the MC. It also hurts the supernatural side of the story, there is hardly an tension built up. Thankfully the Nekomonogatari (Black) arc feels more like the first season but is not that exciting because it is a prequel and the events during "Golden Week" already happend once in the first season.

Since SHAFT will probably animate all the "Monogatari" there will be ten or so more to come so I hope they can keep the level of the first or this will be a painful experience.

Bakemonogatari = 8
Nisemonogatari = 5
Nekomonogatari (Black) = 7