Both games rely heavily on collection. Spider-man is more straight forward with linear levels, but there are challenges (doing things within time limits, killing enemies with certain attacks, etc.) to complete and hidden spiders to find as well. There is a great deal of variety between the 4 dimensions, and some of the boss fights are very cool. The graphics are also quite nice and vibrant, and each dimension's visuals are different. A single playthrough should come out to about 10 hours. You will need a bit more time to unlock everything.
Batman is also a beautiful game, and is more polished and less buggy than Spider-man SD. There were still things I didn't particularly love about it, but the combat is cool, the gadgets are fun, and it's addictive to find all of the riddles and stuff. Batman AA is meant for a true completionist (which I tend to not be, but with that game I was). You will reach a few frustrating and annoying parts, but overall it's a really good game. I don't remember how long it took me to beat, it's probably a bit longer than Spider-man, but not amazingly long.
I've gone for nearly all the achievements in both games, missing only the top medals and hard playthroughs in both (I am lazy to replay games on higher difficulties sometimes). Both games have beat'em up qualities, but Spider-man does it in a more level-based fashion with greater variety and constant action, and Batman does it in a dark and detailed environment where stealth, various puzzles, and exploration are key elements.
moxxidude posted... A year later, Batman: Arkham Asylum is still the same retail price. A year from now, Shattered Dimensions will be $20 at Wal-Mart.
Actually, Batman: AA GOTY in 3D is $49.99 while the standard version of the game is now only $29.99 (Best Buy). I noticed AA went down in price (just like almost all the other games that is released for the 360) within a matter of months.