I recently picked up an iPad 2, and I use it almost solely for gaming. And I have to say that the iPad is a solid next gen gaming device. Personally I think it succeeds where the DS fails. Nintendo had a great idea integrating touch screen technology with gaming, but in the end the hardware limitations and the poor execution of so many games left the touch aspects to be pointless gimmicks in a lot of games. But the iPad with it's fantastic multi-touch screen, beautiful resolution, and advanced graphical hardware really make it a gaming powerhouse. In my opinion it totally crushes any other portable gaming system out there, including the Vita. Here are some games I've been playing the most so far that I think are worth checking out.
ESPGALUDA II HD Smartphone Version
2D shooters are probably my favorite genre, and the first thing I thought of when I got the iPad was how to get Dodonpatchi on there. Well, I was pleased to find that Cave is developing directly for iOS and already has several of it's insane shooters available. Of the group I'd say Espgaluda II HD is the best for the iPad so far mainly due to the graphics. Some of the other releases still have grainy upscaled graphics, which while don't detract from the gameplay, just don't match up to the beautiful HD graphics of Espgaluda. All of their games, however, feature amazing control. I own many dozens of shooters for various systems, but I've never experienced anything like this. Every slight twitch of your finger is registered, which allows you to skillfully weave your character through the intricate waves of projectiles famous in these bullet-hell shooters with relative ease (doesn't mean you're not going to get your ass handed to you from time to time!). It's almost mesmerizing. A slightly more expensive game, but well worth the cost especially considering how much it costs to buy a copy of this for PS2.
Air Attack HD
Another overhead shooter, but featuring fantastic 3D graphics while maintaining 2D gameplay. Featuring a WWII theme that I personally love in shooters (thing Strikers 1945, Metal Slug, etc), great control, weaponry, upgradable planes, and an epic soundtrack that gets you feeling like you are in a Hollywood war movie. A steal at $0.99.
Haven't had a chance to spend too much time with this one yet, but it's graphically very impressive and has great controls. Ditching the virtual d-pad in favor of free controls is a route that a lot of developers are thankfully taking for iOS first and third person shooters. A brand new chapter in the horror series, not a port of the first game. On sale for a limited time for $0.99 from it's usual $9.99, so grab it quick!
Infinity Field HD
I loved Geometry Wars on the DS and it was one game I thought implemented the touch controls well enough to enjoyably play for long periods. And I spent many hours on that game. Infinity Field is very similar to Geometry Wars, with upgraded graphics and sound, and and many added gameplay elements. Fans of GW will love this one, as I do.
Battle Squadron ONE 2-player
A classic Amiga vertical shooter brought to iPad but with a twist. You can play 2-player co-op with an innovative split screen control scheme. Worth it for the soundtrack alone!
A simple but highly addicting game. You circle around an area destroying zombies and saving civilians, but the presentation is very unique. It's almost exactly like a military gun ship display with the somewhat grainy black and white display and targeting system. I play this one a lot, as it's very satisfying to blow up a crowd of 20 zombies with your Howitzer or pick them off one at a time with your Gatling gun.
Puzzle Quest 2
Another game I poured hours into for the DS was the original Puzzle Quest. It's a game that naturally works perfectly for the touch systems. This newer installment is very good, with great sound and presentation, and although I thought the story aspects of the original were more interesting, the added spells and gameplay elements make this a must-have for fans of the original. And if you've never played these games, give it a shot. It's an insanely addictive combination of an RPG and puzzle game, building up your character as you battle various monsters and demons.