I'm really unsure whether to get this game, me and my friend like co-op games, and like GTA IV free roam... but is there enough substance and replayability to make it worth a purchase?

I'd say give it a rent first, then see if you there is enough substance for you.

England sucks for rentals, costs 15 of your american dollars to rent a game for 1 night, I need to know if its worth buying :O

While I haven't played the co-op yet, I hear it's like the best part. I posted a thread giving my first impressions of the game, and it wasn't pretty. But after some time, I've really started to have fun with it. However, I personally wouldn't pay $60 for it, but that's just me. I'm sure there are better co-op games out there that you can play with your friend. Though if you're a big fan of the original, and are just looking for some fun with a friend, I don't think you'll regret buying it. Just keep in mind that the game makes kind of a lousy first impression.

I'd sai give it a rent first, I gamefly'd it and it came today, I think its a pretty fun game, but waiting for a friend to get it for some co-op, its nothing absolutely amazing, but It'll be a pretty fun game to hold you over until other things come out you're looking forward to.

Don't buy this game!! 

Word on the street says this game seriously sucks. I say nay.