The main game that came with my Xbox 360 bundle is Resident Evil 5. I actually finished the single player game pretty quickly - I started playing on Friday night, and I finished it just before bedtime on Sunday. Overall, it's a pretty good game (although I had never played a Resident Evil game before, FWIW). That's not to say that I'm done playing it, however. There are plenty of other things to do.
The game has definitely shifted more towards a standard action game than survival horror - I don't know if that is a good thing or not. I'm not a huge fan of horror movies or games, so I guess for me personally that's a good thing. I could see long-time fans of the series upset by this change, though. There are plenty of big, bad monsters to destroy, though - just nothing where you jump out of your seat due to the events in the game (at least for me).
The events in the game are very much based on what has happened previously in the series. To make sure that I could actually understand what was going on, before I got the game I read up on the series itself. Both the GameTrailers Retrospective and Resident Evil Wikipedia page helped out a great deal. I could see being completely confused by the story if I hadn't done this research before hand. For better or for worse, newcomers to the series would be very confused regarding the events in the game.
One thing that sets RE5 apart from other action games is that you can't move and shoot at the same time. The left analog stick controls your movement, while the right analog stick controls the camera. Once you press the Right Trigger, though, that keeps you in place and now the left analog stick aims your current weapon of choice. While this is a drastic change from other games, at the same time it makes sense - your accuracy is greatly improved if you don't move when shooting in real life, for example. The game does help you out a bit here - most enemies come at you somewhat slowly, and tend to stop for a second or so when they get close. While that isn't necessarily realistic, it does make the game more playable. The controls didn't really bother me that much, once I got used to them.
The other big feature of RE5 is co-op play. The entire game is spent with the two main characters - Chris Redfield and Sheva Alomar. When playing solo, you play as Chris (although you can also play as Sheva once you've beaten the game). In co-op, each player takes one of the characters and you can work together to finish the levels. While I have mostly played solo, the times that I did play co-op were great - I could see that this is how the game was meant to be played. The AI did a passable job at assisting you, but it just doesn't come close to playing with someone else. It tends to go through ammo quickly, and heals you more often than is necessary. It's definitely good that a solo option is in place, though, for those who can't (or don't want to) play with another human. This is available both online and off, and while I haven't played local co-op, from the screenshots it seems like it wouldn't work very well (due to the smaller viewing area for each player).
Once you've finished the main game, there are still many things to do. There are 30 BSAA emblems hidden though the levels (the BSAA is the organization that employs Chris and Sheva). Once you get some of these, you can "buy" various items from the points that you earn for finishing levels - extra costumes for Chris and Sheva, figurines of creatures in the game, and a few other things too. There are also extra weapons to buy, and all weapons can be upgraded (once fully upgraded, you can purchase unlimited ammo for that weapon with points).
In addition, a new game mode is unlocked - Mercenaries. The objective of Mercenaries is to survive as long as possible, and killing as many zombies as you can in the process. This can also be played solo or co-op, however if you're going solo you don't have an AI partner tagging along this time. It's timed, and by default you only have two minutes (I think) to kill zombies. Scattered throughout each level is a time bonus which you can use to add time to the clock. There are also characters and levels to unlock here, too.
Overall, I'm really happy with Resident Evil 5. I could see not liking some of the changes if I were a long-time fan of the series, however given that I'm new to Resident Evil I didn't have any complaints about them. It's a great game, and it looks great too. It's definitely one that I'll be playing for a while. :)