I appear to be the first negative reviewer to have completed the game in its entirety. This game has two distinct parts, the dating sim and the Bad Boys Love secret route unlocked by romancing every bird possible.
The first part is simply too short to be entertaining. Any route can be read in about an hour going at a relaxed pace, but there is significant overlap between routes, including sections that have no effect on the particular route you're playing, so I found myself skipping more and more as I replayed. This also caused me to inadvertantly skip content I hadn't read before, because some sections have multiple outcomes but start out the same way regardless of route. There is no way to go back to content accidentally skipped without reloading or starting a new game and it simply wasn't interesting enough to worth bothering to find out why I was faced with the choice of telling Okosan "convenience store" or "grocery store" and I could infer it had something to do with pudding anyway.
Consequently, there just isn't enough time to give any character depth and there's no challenge to complete a route. By the time you finish a route, you feel like you were merely introduced to the character. Picking routes are also very obvious and there is never any difficulty in seducing the various birds, unless you can't figure out that picking every opportunity to spend time with your desired bird is necessary to romance them. The routes I enjoyed most, Okosan, Shuu, and Anghel, stood out because they were simply the most oddball. For a game that is billed as a comedy, most routes utilize stereotypical melodrama. Bird puns and pop culture references abound, but there's really nothing laugh out loud funny in Hatoful Boyfriend and at best you'll smirk a lot.
There is a very simple stat system, raised by choosing between three elective classes at regular intervals and in a couple of events that likewise present three choices which raise a stat. The stats serve one purpose, which is to determine whether you get a normal ending or an extended ending. Extended endings require you to raise one stat to maximum and reward you with an extra scene that was implied in the normal ending anyway. Each ending has a separate achievement and you can't get both the normal ending and extended ending achievements in one go, so you have to play the same route twice in order to get all the achievements and unlock the Bad Boys Love extended ending. I wasted part of my life to get the BBL extended ending and it was just as disappointing as the other extended endings.
The second part of the game, the Bad Boys Love secret route is much more interesting, but by the time I unlocked it I was already tired of the game. I trudged on in hopes that it would be good and it was, kind of. The game suddenly takes a much darker tone, reveals how the world came to be dominated by talking birds, and becomes a mystery story. It seems interesting for a while, but as all the threads come together it becomes a soap opera for the ages. Characters are revealed to be secret brothers, secret childhood friends, secret enemies, secret agents, secret terrorists, secret weapons, secretly superpowered, secretly alive, but, alas, there are no secret comas to complete the cliche pantheon. I got the distinct impression that the first half of the game was written primarily to introduce the characters so that the meandering mysteries wouldn't simply baffle readers.
All in all, Hatoful Boyfriend wasn't an altogether terrible game, but it just wasn't worth the money and I got it in a 50% off sale. I will likely never read it again and would forget about it entirely if Steam didn't keep it in my library forever. As some consolation, the trading cards were surprisingly valuable and I was able to quickly sell them for about $1.50.
If you don't mind a lot of repetition, love every visual novel no matter what, and really love silly gimmicks, then buy this game. Otherwise, pick up just about any other visual novel on Steam. Even some of the free ones are more entertaining than Hatoful Boyfriend.