First, THIS IS A (+) THREAD. Please do not post something like "Everything LOL".
Justify your reasons (hopefully more than just "I don't like them."), or please don't bother posting. Thanks! 
Common issues I see complaints about are (in no particular order):
Poor players who feel Wizards should be gods.
I've never experienced this, personally, but I know others have. IMO this is really more about the player than the class, but for anyone whose experienced this and wishes to share their story, I'd be interested to hear about it how you feel the issue is the
class and not the player.
Stealing the spotlight from other PCs/players.
I've seen this, but not because the PC was a "wizard" but more so because a player wants to have the spotlight. They make a character which tries to be the best at everything, instead of letting other PCs have their moments to shine.
Being able to overcome just about all challenges.
With many spells Wizards are able to overcome exploration or social challenges in ways other classes just can't. Now, this really isn't exclusive to Wizard, but is more of an issue with spells in general and Arcane spells in particular. Although there are some divine and primal spells, the majority of them are arcane, so naturally seen as the larger issue.
For myself, I've seen some spells do this, but for casters they need to know or have the spell prepared--and I have seen often enough a player lament
not having a spell which would make things easy to overcome. I just don't see this in actual play, so I would love to hear
actual examples and not just white-room/theory-crafting.
Too large of a spell list.
Now, this one I agree with, but probably not for the same reason others might. IMO probably half the spells are useless and/or pointless--or just outright silly. 90% of the spells I see are almost always the same ones. I just don't think we need so many.
Too many spells in the spellbook.
I agree with this in the idea that wizards gain
TWO spells per spell level to add to their spellbook. I think one would be better, and acquiring more would be through finding scrolls or spellbooks, research or downtime activity, etc. with rely more on DM fiat. Alternatively, allow two but re-instate a system for actually learning a spell, so that wizards don't necessarily always learn the spells the player wants--at least not on first try.
Cantrips are an issue.
I see different thoughts on this:
1) Combat cantrips make wizards boring
pew pew all the time. Magic is less magical. (Along with this, but perhaps a separate issue, even utility-type cantrips can make magic feel less magical).
2) The opposite view: being able to
pew pew is more magical than firing a crossbow when running out of spell slots.
3) Cantrips such as light and dancing lights make environmental factors such as darkness a non-issue.
Spells are too powerful.
Not a common complaint, of course, but one I agree with. Arcane spells especially seem to outstrip the relative power compared to other spells, and certainly compared to what non-casters can even attempt.
The class is boring. (@Zardnaar)
Player Expectations. (@James Gasik)
So, I sort of get this one. But IME it isn't so much about "wanting non-magical classes to be unable to do likewise" as it is about keeping the game grounded. Also, IME spellcasting-players rarely care as much about the more mundane tasks, such as setting up a campsite.
Hardly anyone plays Wizards anymore. (@Ruin Explorer)
This isn't something I've experienced personally as Wizard as a class is played about as much as any other class in my games (or ones I play in). However, I certainly understand how people joining D&D and wanting to play a pop culture Wizard would be disappointed.
I'm sure there are more, those are just the ones I can think of at the moment. I'll update this list when people add things I didn't think of.
Again, I am really interested in
actual experiences in real game play if you have an issue.
This is not meant to be a "Wizard-bashing" thread, but more of an attempt to identify actual problems instead of theoretical or white-room.
