Dead Rising has quite a bit more going on with it than your impressions. The thing that makes the series so special is that it has incredibly fun gameplay(killing zombies in hundreds of ways) yet balances it with some very demanding time limits and missions that require you to learn how to balance your time and so on. There's really nothing else like it and the comparison to Dynasty Warriors is quite silly as DW's combat system is exponentially deeper and it's a combat focused game but that's another story.
Brad is just running around and finding collectibles, leveling up, and having fun similar to how one would roam GTA V's world. There's much more to the game.
Alright. I do like the concept of combining two disparate objects to make zombie killing weapons (gives me, oddly enough, Kirby: Crystal Shards vibes). I should get a Dead Rising game one of these days.