The larger screen(s)
Obviously this is going to be the biggest perk, what with the whole "XL" thing going on. The screens on the 3DS XL are 90% larger than those on the standard unit, and that makes a huge difference. Opening one up is awe-inspiring - the top screen is larger than the Vita's by a good amount, and once you turn it on, you'll be blown away by how incredible it looks. The 3D, too, is improved with the enlarged screen size, even if some claim to have a harder time finding the three-dimensional "sweet spot."
3DS games look absolutely wonderful on the enlarged screen, and though they're a little stretched out (the resolution hasn't been improved with the screen size increase), it's never distracting, nor does it take away from the wonderful, massive screen. The bottom screen, too, greatly benefits from this expansion, making it easier to use than ever. Oh, and the system's bottom screen doesn't leave smears on the top screen when it closes anymore - a small note, sure, but it's a nice touch, and a welcome change.
The nicer form factor
Some complained that the original 3DS was a little small, leading to cramped hands after long gameplay sessions. The 3DS, with its much larger form factor, doesn't fall victim to this folly - the massive handheld should quell any concerns for those with large hands. In general, this means that the system is much more comfortable to hold and use, thanks to increased spacing between circle pad and button positions.
The rounded edges of the system are also nicer, letting the system rest comfortably in the palms of your hands instead of digging in, as the original 3DS does. It doesn't make a huge difference for quick pick-up-and-play games, but if you're someone that wants to hunker down and carve through an RPG on this thing, then this ergonomic factor might be something to consider.
The (slightly) better battery
The original 3DS's battery has been lauded as one of the system's greatest shortcomings, lasting a paltry three to six hours. The upgraded 3DS XL, on the other hand, packs anywhere from three-and-a-half to six-and-a-half hours, giving you a solid 30 minutes more gameplay.
It's not much, but it'll do for now. We were worried, initially, that the larger screen might lead to a worse battery, so we were happy that, in our tests, it outperformed the original system, albeit slightly. Battery life will obviously vary depending on the game, the screen brightness, and a bunch of other factors, though, so you'll still drain the system's juice quickly if you're not careful.
That DS games look lower res and washed out
DS and retro games, in general, don't look great on the 3DS screen, and the 3DS XL does them no favors. We tested out some original DS games and noticed that they were slightly blurry, and looked a little washed out. It wasn't a deal-breaker, obviously, and it didn't stop us from playing an hour of Tetris because we totally lost track of time, but make no mistake: the 3DS still isn't the ideal system for playing DS games.
If you're looking for that, grab a DSi or the DSi XL, which not only makes DS games look wonderful, but it does it with a better battery life. Don't let this be too much of a deterrent, though - they still look fine.
It's not a real 3DS redesign
We know that plenty of people said they were holding off on buying the 3DS XL because they were waiting for the hardware upgrade. While this is, technically, a hardware upgrade, we don't think it's the one anyone expected. You were waiting for the 3DS Lite, right? Well, this isn't it.
Hardware-wise, these upgrades are minor. Besides the new size and a few modifications, it's the same 3DS that launched in 2011. We're feeling sure there will also be a full-fledged upgrade down the line, and we figure you might be as upset as we are that this wasn't it.
It's a little heavy
Though it's definitely a more comfortable system to hold, and the more ergonomically-friendly design makes it better for longer play sessions, we did notice that the system felt heavier in our hands the longer we played. If we leaned it on our knees or a table, it was less of an issue, but holding it up for a long period of time made our hands tired.
It's a trade-off, sort of, since you're not going to get hand-cramps like you did with the original 3DS, but the added weight has the negative boon you'd expect: it makes it heavier.
Should you buy it?
If you already have a 3DS, we'd say hold off, no matter how painful that might be. Sure, your games would work, but you'd need to buy new accessories (your case and Circle Pad won't fit), adding extra cost. The bigger screen and the enhanced 3D will definitely make your games look better, but let's be honest - there's going to be another 3DS upgrade, and it's going to be about more than size.
If you don't have a 3DS, this is as good of an excuse as any to pull the trigger. Sure, there's likely going to be another, better, newer 3DS within a year or two, but this should hold you over until then, and it's unarguably the better version of the handheld. And besides, it's not as if your friends and relatives haven't "inherited" your old Nintendo hardware before, right?