Contains minor spoilers.
Disclaimer- I rate manga relative to others, so 50 is average, 60 is a little above average, etc. My score does not mean that this is a bad manga. It is, in fact, quite a fun read.

I've got to admit, I'm not too huge on shonen romcoms. Some of them are good, sure, but a lot of them fall into the same old tropes, use similar jokes, and/or have bland characters. I started Girlfriend, Girlfriend expecting the same kind of generic romcom that's so prevalent in Weekly Shonen Magazine. I wasn't entirely wrong, but Girlfriend, Girlfriend has a few things going for it that made it fun- likeable characters (for the most part), a stupid premise that gets played seriously, and, above all else, a sense of humor based around making fun of itself and harem romcoms to the point where it may as well be parody. At least, I think it's making fun of itself, could entirely be lazy use of tropes played so seriously as to look like parody. Hard to tell. Either way, it's great.

Girlfriend, Girlfriend is the story of Mukai Naoya, a dude who asked a girl (Saki Saki) out repeatedly until she finally accepted. Apparently it's a pretty good relationship and they both like each other a helluva lot.
Do not try this at home, ladies and gentlemen. This is how you get slapped with a restraining order.
Anyways, the relationship is great, yippee, until one day Naoya is confessed to by another girl, Minase Nagisa, who has apparently dedicated a significant chunk of her life to making herself into an ideal girlfriend for Naoya.
Again, don't try this at home. You are not living my the laws of manga. This is how you get slapped with a collapse from exhaustion. Also, it's borderline psychopathic.
Naoya, being a stalwart and devoted partner, doesn't want to cheat on or ditch Saki Saki. Naoya, being a horny teenaged dude with a bleeding heart, also doesn't want to reject Nagisa. Naoya, being an absolute genius by harem romcom standards, comes to the obvious correct conclusion, and asks Saki Saki for permission to openly two-time her.
I will not attempt to advise you on that one.
The story is a pretty standard romcom from there, just kind of meandering through the main characters' lives, but, to its credit, it's so blatant and in-your-face crazy that it's funny. Naoya is a valiant blockhead, sort of a mix between a stooge, your kind and helpful neighborhood kid, and that dumb dude in every B-list romance flick that has the social awareness of a goat's toenail. Saki Saki and Nagisa, while marginally less dumb, create a comedy trio that's like straightman humor if the performers were all so dumb they couldn't remember if they were the funnyman or the straightman and wind up switching roles constantly. It winds up being genuinely funny and often taking romcom tropes and playing them like a comedy act. It's pretty impressive semi-parody, in all honesty. Also, there's not fanservice up the wazoo. Might be an upside to you, might be a downside.

When it comes to harem romcoms, they kind of need likeable characters. Suffice it to say Girlfriend x 2 has dumb enough characters that they're endearing. Naoya's brand of socially unaware honesty is pretty good, and the fact that the other characters are idiots as well really helps make the comedy side of things funny. Saki Saki and Nagisa are decent, and they've got a genuinely sweet relationship with Naoya, which is nice since the series could've easily gone for NTR. Decent characters, overall.
Except one, who ruins nearly every scene she's in with starting stupid arguments, stalkerish tendencies, and just generally being annoying. I'm sure she has fans, but for me the manga would have been better if it had approached her characterization in pretty much any other possible way.

As befits a romcom, most chapters are just random bits of the characters' lives, with visual gags and stupid jokes. Thankfully, Girlfriend, Girlfriend, either cleverly or through sheer lack of creativity, decides to eschew making particularly unique stories and instead has dumb romcom tropes played completely straightfaced. Constantly. It does do a good job, to be fair, but at points I feel like I've read the story a dozen times before. Still, it's either genius parody or so horrifically unoriginal that it looks like parody, but either way, it's fun. It's hilariously dumb. It's worth a read.

Yep. Definitely worth the read. I'd imagine a lot of people will hate it, but for me at least, it's a truly stupid fun series. Well written, touching, a great story? Not especially. Still, the important thing is that it's entertaining, and it's hilariously stupid enough to be just that. As far as harem romcoms go, this is a standout.