the internet's opinion is that a vast majority of the things you probably wouldn't notice yourself are deal breaking, system ruining flaws that should make you regret your decision and purchase. just buy what you can afford/want the most/pin the tail on the laptop screen.
DS and virtual console games look really bad on the 3DS XL. If you want to mainly play those games, id suggest you not get an XL. I tried to play pokemon heart gold and not only is there black bars but its all stretched out and pixelated/ugly. Very noticable.
On the original 3DS, if you held Start and Select while starting a DS game, you view it in it's original resolution. Does that work for the XL?
It does, and it's 1:1, so the picture is really nice. Sometime I play this way, when clarity is needed or preferred, and other times I'll play with the bigger more blurred image when I need the real-estate. Either way isn't bad, and not a deal breaker, but all 3 have their pros and cons.
The only DS games I've played on my 3DS XL have been Professor Layton and the Unwound Future and Etrian Odyssey. They both looked just fine though they aren't exactly the two best games to use to judge this.
Since both games have so much text, that was a great improvement (even though Etrian Odyssey's horrible font still made it somewhat hard to read at times). Neither looked pixelated or stretched or anything like that.