Is a 4 yr education at Waseda SILS worth it?

I'm applying to the September program next year and a lot of reviews say Waseda is overrated and not mentally stimulating. Most of the teachers lack the ability to speak English. Since I am from abroad, I need to make sure Waseda is absolutely worth it, since I'll be paying a huge sum.

I want to specialize in International Relations, what is your opinion about finding employment as an international student if I complete the course?

I might agree with the overrated part. It is considered to be one of the best universities in Japan, its alumni network is very strong in terms of unity, some say they're like a religious group or something, lots of successful alumni in many fields and different sectors, sports teams are excellent you'll have fun cheering them as a student and an alumnus, a typical Japanese person without any international background would say that getting in Waseda basically makes your life, it's literally one of the best schools you could end up in in Japan, but then this is all in the Japanese sense (a small world). SILS from what I recall is a relatively new school, and with English still being not as common in Japan, they probably struggle getting professors who speak English and are actually good.
To get to the point, if you are an international student with funds and are looking for the best, you should probably look somewhere else lol. If I were you I wouldn't do it.
May I ask what other schools you're looking at? and what made you want to look at schools in Japan?

I guess it depends. If after graduating and going back to your country your focus will be to do a career in asian business or the like, I think Waseda will stand out pretty well just for the name and prestige.
For anything else, it'll be just like any other university and chances are that many don't even know it.

But, if you decide to stay in Japan, Waseda is basically like a free pass to get a job (not literally, but it makes things much easier...)

Anyway, in Japan, universities are mainly about reputation. If you got into Waseda, or Sophia, etc., for employers this doesn't mean that you're more intelligent or better prepared than others, it means that you really sweated your ass to get in there, and that makes you more "honorable" and "trustworthy" (words from a japanese colleague).

Anyway, if you just want to know whether the school has a good level or not, honestly, it is..mehh. You'll have minimal work to do, people sleep during class and somehow still pass the course.... as I said, it's just getting admitted that requires a lot of extra effort.