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I won't look worse then mavericks, but they did optimize it for retina displays.
 
I have a 27" iMac and the system font, Helvitica, definitely looks worse than Mavericks. I'm hoping that will change by the time it's released to the public.
 
I have a 27" iMac and the system font, Helvitica, definitely looks worse than Mavericks. I'm hoping that will change by the time it's released to the public.

It won't, that's the font they went with. You can change it back to LG if you want.
 
There have been many reports of problems with Yosemite and text on a non-retina display. I haven't done any side-by-side comparison with Mavericks, but when using an external display with my rMBP, I didn't experience any issues. Sure, the retina display looks much nicer, but it has always been like this. Best thing would be to go to an Apple store and check it out on the display, before installing it on your machine.
 
Unquestionably optimized for Yosemite.

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I'm sure that Yosemite is not installed at any Apple Stores at this time. Not at least for 1 more week, it won't be.

There have been many reports of problems with Yosemite and text on a non-retina display. I haven't done any side-by-side comparison with Mavericks, but when using an external display with my rMBP, I didn't experience any issues. Sure, the retina display looks much nicer, but it has always been like this. Best thing would be to go to an Apple store and check it out on the display, before installing it on your machine.
 
Sure, the retina display looks much nicer, but it has always been like this.

As far as I'm aware, Lucida Grande was a font specifically optimized for display on (low-DPI) computer displays, whereas that's decidedly not the case for Helvetica (Neue), especially at low font sizes. Thus one would expect to have it look at least somewhat worse (whether that's an issue, is a whole other question). I'm almost certain Apple would never have switched to HN had it not been for Retina displays.
 
At this point, it has been refined a LOT from earlier betas....and looks quite good on non-Retina displays.
 
Looks fine on my 27" iMac. However, Dark Mode is definitely optimized for Retina. The menu fonts look like ass on my MBA and iMac, but look fine on my rMBP.
 
Yes. Apple has font differences and transparency differences between the two different types of displays.
 
Helvetica Neue looked pretty "meh" on my mid-2012 cMBP in DP1, but it's been refined quite a bit since then. Looks great now, in my opinion.
 
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