The reasons people hate Patch 5.16
My honest reaction the the Juggernaut changes was to jump up and go run a couple miles (literally), but so far the general response of the forums is that everyone hates everything and in a much larger amount than the hate patches normally generate.
Now some would argue that the fact that there is so much more rejection of this patch proves that this patch is flawed, however it really doesn't. The main cause of the large amount of hate is simple that the patch itself is such a massive undertaking. One thing you will notice looking through the forums right now is that each post complains about one particular aspect. A few people hate the garen changes, a few people hate the skarner changes, a few hate the mordekaiser changes, and a few are against the item changes. (Apparently everyone is cool with the darias so gj there i guess), however there isn't really anyone who has complaints about everything.
Normally there are only a few major changes per patch. Minor buffs and nerfs don't typically elicit a strong response. As 5.16 has been shown to have many more large scale changes than the average patch, all the same groups as normal are complaining about the patches, but more have been drawn out because of how many different large changes are being made.
One other thing I have noticed is that the majority of these posts are being made by people who say that they either main these champions, or just love them dearly for what they are. A common misconception these people seem to have though, is that by maining a champ they can tell exactly what is wrong with the champ and how to fix it. They are also upset that things they like are being changed. Now of course, having experience playing a champion is valuable, but it is not the real way that you figure out how to fix it. Even if you do main a champion, can you honestly say that you have spent hours and days experimenting with and attempting to think of solutions to fix the champions problems? Most likely no, but the people who work at riot can say that.
Another reason that maining a champion is that you are biased. The mordekaiser main with 1000 games on him may know mordekaiser better than anyone else, but that same person also liked the champion for what he currently had despite any problems. Another few million players disliked the champion. These changes may upset that dedicated mordekaiser main, but they aren't made for him. They are designed to make the champion more appealing to the general player base while trying to have him live up to their own vision for what he should be.
Finally, remember that pretty much no one on the forums complaining has actually played any of these changes yet. These complaints are based purely on whats on paper (or i guess a screen). I highly doubt that anyone was able to read the changes, jump on their Pbe accounts, play enough games to determine that this champion has been gutted and then write several paragraphs about how terrible riot is.
Call me a fanboy defending riot till the end if you want, but that's what I have to say about the matter. I personally like the look of these changes. I have been playing top lane (as well as a good deal of jungle and support) since I started playing league. These are items I have been building for a long time and these are some of my favorite champs being altered here. Garen was the first champ I hit Mastery Lvl 5 on and Darias is currently 3rd out of all the mastery points i have gained. I can't say I main either morde or skarner, but I have always liked them as champions even if I have thought that they needed some work. I am quite excited for the patch despite changes to things I enjoyed.
So in the mean time, players enjoy the game and Riot, keep up the good work.