Mr. Outlaw's reasons are subjective
Grip angle - subjective
It's ugly - subjective
Reliable - it is very reliable. Although I have other pistols just as reliable. But the Glock is reliable
Shitty sights - I agree. I don't like the sights, but Glock is one of the easier sights to replace and there are a lot of choices for aftermarket sights
Aftermarket parts - there's a crapload of parts available for Glocks. Sights, triggers, holsters, WML, etc.
Although I am a bit of a fanboi, I'll admit that there are better pistols out there. I'd like to try some Walrher's and some Canik's and others. Competition is a good thing
That's kind of how opinions work -- they are usually subjective.
He's not telling anyone to not buy Glocks. He's just saying people buying their first pistol might want to think outside the "Glocks." (I just made that up,

)
The 5 points he raised are valid. Most who compare Glock designs to other popular models have made the same observations. While still a matter of preference, he makes valid points about grip angle being different than most other pistols that follow the 1911 grip angle -- arguably the most ergonomic and natural angle for a pistol grip.
He offered his own anecdotal stories about poor customer service and reliability. Having a gun shipped back to him with no repairs for a cracked frame seems like a valid complaint, as does his experience with ammo that malfunctions in his Glocks that work perfectly in other brands.
As I said, I agree it's subjective, but that doesn't mean someone else's opposing opinions aren't just as subjective. Hence, the recommendation to not get locked into buying a Glock first before looking into others you might like and shoot better.