Discovery is a great side scroller in the AC2 universe and should be owned by any AC fan or platforming fan.
The Bad: Acrobatics aren't the easiest to do, gets very hard towards the end, can't really see where you're going, feels repetitive
Assassin's Creed is an amazing franchise, and no one would have thought it would ever go to portable systems, but it did. Discovery follows Ezio in a 2D side scrolling adventure that plays out fairly well. The story doesn't really have anything to do with the console game except following the Templars plots. Ezio must help Christopher Columbus get funding for his expedition to the new world, but the Templars are foiling his plans.
The game controls fairly well with you just moving left and right. Ezio can jump, climb walls, attack, throw knives, and even sneak his way through levels. The levels are fairly large and some even have multiple objectives so you must climb your way around the platforms, kills guards, and pull levers to find your destination. Wall climbing is fairly simple with the press of the B button. Like in the console game you can pull enemy of ledges that you're hanging on, hide in hay stacks, barells etc. While climbing walls are easy it's also the most frustrating part since during tight situations you will try to jump on a wall and you have to press B again for Ezio to cling on. You never quite get used to this (especially if you've played the console game) and it can lead to cheap deaths.
Fighting is just like the console game which is a counter attack fest. Holding R lets Ezio block and pressing Y at the right time will let him counter. It's familiar with the console game so it won't freak you out. The best way to avoid confronting guards in these fights is using your mini-map on the bottom screen. They show up as yellow arrows and if they get in your field of vision (the black square around you) they will see you and alert nearby guards. Throwing knives before they see you is good as well as waiting for them to turn around so you can run up behind them and kill them just like in the console game.
Later on all this gets more difficult and becomes hair tearingly difficult since you can't always see the next jump ahead of you and you can plummet to your death far away from the next checkpoint. There are multiple kinds of guards and you will get the harder ones thrown at you more often in the last few levels. Navigating around these guards is some times impossible and you must fight them due to the level setup. While these levels are hard all the ones before that are pretty fun and it's satisfying to jump up from a ledge and land on a guy without him seeing you.
While there are different kinds of objectives you can blow through the game in about 4 hours. If you have a DSi you can take a picture of yourself and it will be put on a wanted poster like in the console game. Tear 10 of these down and you get a permanent health increase. Collect orbs throughout the game and buy Animus hacks to use when playing through the game again to increase your score. This adds to the replayability for people who really dig this game. The graphics are pretty good and look nice in 3D but there's really not detail to it. The voice acting is good, and the game's just overall fun to play and worth a play through.