I'm reviewing a site design and the hero image has a font size of 53px, which feels uncomfortably large, especially for longer titles.
Is there a limit to how big titles should be on the web? i.e. are there any guidelines around this?
What would be helpful to the designer is if you can tell them why it appears to be uncomfortably large, in your estimation. Often, I find that it's not the actual point-size of the text alone that makes it uncomfortable. Off the top of my head, here are some reasons why a large font size might make the text seem uncomfortable to read:
To your question about existing standards for type sizes, the answer is no, I don't think there are any standards for upper limits to point size. (There are accessibility guidelines that describe a minimum legible font size, though.)
It never hurts to voice your concerns, and let the designer decide how to address the issue. (The whole point of a critique is to improve the work, after all.) Don't forget, there is probably a reason they made the hero text that big, so provide as much detail as you can about the problem, but try not to be prescriptive about the solution.
If you're looking to read up on this further, I recommend starting with the article "Responsive Typography: the Basics" by iA. They do a pretty good job of explaining the variables involved with designing typography for the web.
From a cognitive perspective what matters is the size of the projected text on the retina, which involves:
So there isn't really a gold standard, what will appear small to some will appear large to others.
Obviously, this doesn't apply if you know the screen size/resolution/position like you would with airport information screens - there you can work out legibility based on distance.