forza is cool, you can race and drift with friends when your bored playing singleplayer. the car and track selection is limited. you can buy car packs for 10 bucks or season pass for 50. they really need to add more tracks, they didn't even include nurburgring... fucking bummer and a half. the one thing i noticed is the crowd still look like 2d cardboard cutouts... really fucking lame for a "next gen game".
dead rising is cool. the story can be completed fairly fast. there are add-ons for 15 bucks a pop or 50 for season pass.
i think forza has more replayability if you have friends that play it. there are racing communities that have events to keep things lively. redditors have a league, Reddit Forza Racing League. i was in ETCC, pretty laid back and friendly, run by brits.