New M.

For starters there are too many restrictions placed on non paying members. It's the most ridiculous business model I've ever encountered. As a free member you're entitled to a profile and three messages and three profile comments a day. If you receive four messages in your inbox the fourth one is automatically deleted never to be read again. There are plenty of crazy pervert scammers, so your inbox will fill up quickly and unfortunately anyone genuine responding to your profile will likely get lost in the shuffle.
Plenty of people will try to use the comment section in your profile to carry on a conversation with you but if you've already exhausted your limits for the day it could take awhile to exchange emails and get the pen pal relationship up and off the site. That sucks, if you're going to have a social site then communication should come easily. Some users bypass this problem by including their email address in their profile, but that's not my scene, at least PPW is fairly good about dealing with scamming or abusive users, I wouldn't want to have to sort through all that spam in a throwaway inbox.
One of the most annoying things I've found with the site is that you can't even delete emails that you've already read! I guess that's for paying members only? How cheap is that? And what members? This site has very low user inventory. Not many people are ever online. Again, it's such a hassle to be a member on the site, if there weren't so many restrictions I'm sure more people would sign up creating greater user inventory. There are literally zero incentives to have a paying membership. You pay something like $10 USD a month to get emails from spammers and to wait and hope for a few more real people to sign up. The site even looks like it was made in the 90s, the user interface is horrible and not well organised, unlike Interpals, PenPalWorld has messages, users and friend requests hidden under various tabs. It's not intuitive at all, it's confusing. Even marking your marital status isn't in your profile (which would make sense) it's under your account information but it's visible on your profile when people search for you -figure that out!
Overall, I would never use or return to the site unless they dropped the paid membership and cleaned up their UI.

I'm going to preface this review by saying that IP was never perfect to begin with. However, there's an obvious decline in both the activity on the site and the quality of its members.
I've been on and off IP for probably ten years. In the earlier days when I was on there were still scammers and pervs, but I could find a pen pal very easily. I would always have several people that I could carry on conversations with, nothing deep or long term, but satisfying none the less. I would have so many offers that I had to decline a few just because I was already busy with other pen pals.
Flash forward to today and my age (I'm in my 30's), coupled with the decreased number of *real* IP users, and a month of waiting, I didn't get so much as a single message. Mind you I was quick to lock in my filters, these filters allow you to block individual countries and select age and gender restrictions. It would perhaps be easier to select the countries you do want to hear from because sadly so many of them are flooded with fake users. That being said, I wasn't so restrictive that I blocked everyone, just the men.
This site, I believe, favors the young. The older you get, the fewer members you have to choose from. There are plenty of young users here. Many users are actually fake, they're fairly easy to spot, they often choose English speaking countries for their profiles but they speak in broken English about generalized topics. They like to steal photos from iStock or off of social media, a quick image search usually reveals whose faking.
There are many scammers looking for sex/nude photos, money or to give you a virus (the forums are apparently crawling with them). There are also weird people who want to marry you, push their religion on you, and one elderly woman even claimed that people were asking her to adopt them! Damn.
There are easily 20 profiles faked every hour, that adds up to a lot of users, so don't be fooled by the numbers when it comes to how many are "online". There are twice the number of men on the site compared to women, perhaps this is why so women feel hounded on IP? Do men no longer talk to other men? The majority of people pefer to speak to Americans, the British, or the Japanese (apparently no one gives a damn about Canada lol). A lot of countries aren't considered desirable or popular, which I'm sure is a drag and might feel a touch isolating.
Sadly Interpals has become more of a dating site with most *real* users looking for love and marriage. Others use the site explicitly to boost their social media followers by linking to every imaginable platform including Etsy.
Aside from all of the above, the site is glitchy, my profile would disappear from search engines and then reappear for no rhyme or reason, which didn't help for being found by anybody. I also had very few people visiting my profile, and only ever when I was logged on. I never had offline views, and maybe averaged about 2 profile views a day (whenever I was online which was fairly frequent).
If you're interested in using Interpals make sure your pen pal requests are clear, set your restrictions, speak fluent English (enough to converse) or simply speak in your own language. Set boundaries and do not share your personal information! And I guess most importantly... Cultivate patience because it may take awhile.