The first "Diary of a Wimpy Kid" was about going to a new school and trying to fit in. An idea that's been used quite a bit and is handled decently while being embarrassingly humorous at times; well aware of its own silliness.
The second film, "Rodrick Rules", has to do with more with the brother and main protagonist of this trilogy, Greg (Zachary Gordon), butting heads and not really getting along. At the same time, Greg is crushing on a girl that just doesn't seem to be aware of him. Again, handles some mundane topics only this time with more silliness and more embarrassment to the point of self-satire.
In this third entry of the "Diary", school has ended, it's summertime, and Greg is still dealing with his crush. Only difference is now his dad starts to work his way more into his life [story]. Or, at least he's trying to. Now Greg has to find a way to connect with his father before school starts up. Worse case scenario, he gets sent to a boarding school to finish out the last five years of his education.
Now, I like these movies for the what they try to do while still keeping in mind that kids are the target audience. The Diary movies are do the same thing and it doesn't get old, but it does get sloppier down the road. "Dog Days" shows how. It takes the coming-of-age story of Greg Heffley and makes it less coming-of-age and more about keeping the state of this character [and apparently the actor, too] through a non-maturing and straight-lined journey.
What got tedious in the previous installments were what the target audience wanted to see the most; all the over-the-top ways Greg seems to be able to embarrass himself. And every new one is either something we've already seen in other movies or something we've experienced ourselves. Either way, Greg seems almost destined to be the bad-luck magnet anywhere he goes.
In case you're wondering how the crush and daddy issues go, they don't. Greg and his dad never had enough screen-time together in the first two, maybe intentionally that way to set-up the threequel, but it never occurred to me there was no bond between them. The movie drags this discomfort of them not seeing eye to eye for about 80 minutes making sure it isn't the main focus; a movie that embarrasses its main character every 5 to 10 minutes with summer-themed hijinks. Such classic 13-year-old shenanigans as sneaking into a country club, accidentally getting your best friend's dad thrown to the ground and handcuffed by the police, and of course, staying in a swimming pool for several hours because your swim-trunks got stuck on the diving board.
Because this movie is a sequel it has it's share of problems most sequels face when trying to do something new. Most of the recurring characters come back to do very little and are often there just to keep the casting list shorter. Other times they're brought in just so the audience can remember they forget about them.
The first "Diary" did such a good job at introducing character and giving them each plenty to do that's it's pitiful most of the ones that returned hardly do anything now. It's sadder to see how much this movie runs in circles to the point where it eventually becomes self-aware and tries to switch tracks... in the last 15 minutes. Everything that seemed like a dilemma wraps up hastily in these last few minutes without much build-up or inspiration to resolve. It just happens because the movie [and trilogy] is almost over.
In conclusion, "Dog Days" takes what worked in the first movie and what didn't really work in the second movie and slaps them together, trimming off any promise it might of had. The embarrassing moments are there and so are the dilemmas no mattered how badly wither are tackled. It's watchable, but not re-watchable.