The devil is in the details. I see lots of builds that have nice numbers on paper but perform poorly.
FWIW I have the following and it runs great and looks great:
- Intel Core i7-930 2.8GHz
- ASUS ROG Radeon HD 5870 Platinum MATRIX 5870 P/2DIS/2GD5 Video Card
- Mushkin Enhanced Redline 6GB (3 x 2GB) 240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800)
- ASUS Rampage III Extreme ATX Intel Motherboard
The thing here is that memory has really fast timings and the mobo is fast too and the video card has gobs of memory.
Since the game was also made to run on Xbox and (presumably) look pretty good on that I think any competent PC should be able to manage and look pretty good.
The game is all first person except when you use the cover mode (i.e. hide behind a box or something). The transition is seamless and works really well. Indeed the move to third person when in cover is great. You’ll be glad for it.
I am only on my first playthrough but every review I have seen suggests a high level of replayability. Some reviewers finished the game then compared game notes with another reviewer. They were surprised to see how different their play was and the things they missed. Even though they “missed” stuff they never knew it and their playthrough felt complete.
As I mentioned earlier there is an achievement to play the game without killing anyone (except boss fights where it is unavoidable). Presumably that is possible and I think it’d be fun to give it a go.
I have heard 20-30 hours if you work hard at going as fast as you can. If you spend time looking for side quests and exploring probably more.