Halo 3 is a great big lump of FPS fun. The graphics are cool, especially the lighting,
The lighting is solid. Obvious its a great game. I have to yet figure out why Halo has so much hypre surrounding it. I really don't know. There are better games, quite literally. Halo was an exceptional Console FPS.... but, that's about it. There was nothing of any actual note about on any level that I ever found, it was always very cut dried and simple. Nothing challenging or interesting.
I'm not one of the people that go out screaming that Halo sucks. Halo's a fine game in its own right. But it's incredibly odd that it's so succesful when games just as good, and some far better, don't do nearly as good as it.
Halo's worst aspect has always been its fanatical fan base. Try talking to one of them sometime. It's scary. Really scary. Like... they should be locked up in a solid metal cell and never be exposed to anyone ever type scary.
Oblivion improved on nearly all aspects of Morrowind. It definitely has flaws of course, psychic guards being one and level scaling being another, but it's still a pretty cool game. The stories are immersive and the huge amounts of quest options mean that if you don't like one quest line you can simply do another.
For every improvement over Morrowind, it also managed to do something worse than Morrowind. The story, with the exception of some of the side plots (like the Dark Brotherhood), was shallow, predictable and boring. For all its pretty graphics it was an incredibly uninteresting game compared to previous entries in the experience. It had none of the alien appeal of Morrowind. Voice Acting is meant to be a plus, not a minus, yet most of the Voice acting in Oblivion, with very small exception, ranges from awkward to just plain horrible.
Assassin's Creed is 75% pure awesome. Towards the end repetitiveness kicked in and the last level is particularly frustrating. But for three quarters of playing, all I could think was 'whoa'. Again, it isn't perfect but that doesn't mean it's crap.
I actually liked Assassin's Creed well enough, not perfect by any stretch... but it definitly had its amiable qualities. Overall I felt it was one of those games that should have its positive aspects taken out and applied to other games. There are several RPGs where, if you made some of AC's aspects stat based... you could finally have RPGs with more interesting thief/rogue/assassin type characters.