Because there's some funny and entertaining moments.

Its rather amusing to watch him.

^^^
well i played alot of the games he review, i had alot of memories with them and he just goes and tell me how shitty the games are.
lets face it they are old outdated and old games are DIFFICULT compared to now.
hes just too dramatic.

Some of his jokes are funny, some are not.

There are people who've done the schtick better too like this guy:

I don't know why but this video always makes me laugh no matter how many times I see it.  ****ing goombas...

Nostalgia.

I find it funny because he overdoes it so extremely on purpose and those games are truly shitty and I recognize the pain of playing them form childhood.
He's certainly just as funny as most "funny" men in films today who only make noise (being noisy and dumb is apparently funny) and make dick and gay jokes half the movie.

A lot of times his foul language rants are very funny and very unique.

A lot of people use the word F#$% out of place, to the point where it loses it's impact. The way he makes use of it is pretty hilarious.

On every video he does give you a lot of good background information on the systems, games, and companies.

Plus the games are so hilariously bad you can't help but laugh.

Everybody thinks differently, whats funny to some people is lame to other people, what's fun for someone is boring to others. You just don't like this type of humor, but many people do.

because he's entertaining

One more thing I actually enjoy since I'm a huge nerd, is the trivia and stuff he tells you in many episodes. Its interesting to me, and the mix of that and the outbursts and silly stuff makes it very unique as well.

Bitches don't know about Spoony.

http://www.spoonyexperiment.com/